The existing code used the magic number -1 to represent the absence of
a status_type in the extension. This commit replaces it with a macro.

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Because extensions were keyed by type which is sparse, we were continually
scanning the list to find the one we wanted. The way we stored them also
had the side effect that we were running initialisers/finalisers in a
different oder to the parsers. In this commit we change things so that we
instead key on an index value for each extension.

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Remove some functions that are no longer needed now that we have the new
extension framework.

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

The _clienthello_ in the extensions parsing functions is overly specific.
Better to keep the convention to just _client_

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

This lays the foundation for a later move to have the extensions built and
placed into the correct message for TLSv1.3 (e.g. ServerHello or
EncryptedExtensions).

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Later we will have client extensions code too.

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Add support for construction of extensions

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

This builds on the work started in 1ab3836b and extends is so that
each extension has its own identified parsing functions, as well as an
allowed context identifying which messages and protocols it is relevant for.
Subsequent commits will do a similar job for the ServerHello extensions.
This will enable us to have common functions for processing extension blocks
no matter which of the multiple messages they are received from. In TLSv1.3
a number of different messages have extension blocks, and some extensions
have moved from one message to another when compared to TLSv1.2.

Perl changes reviewed by Richard Levitte. Non-perl changes reviewed by Rich
Salz
Reviewed-by: NRich Salz <rsalz@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>