This patch adds support for the evaluation of TCP flags in nwfilters.

It adds documentation to the web page and extends the tests as well.
Also, the nwfilter schema is extended.

The following are some example for rules using the tcp flags:

<rule action='accept' direction='in'>
    <tcp state='NONE' flags='SYN/ALL' dsptportstart='80'/>
</rule>
<rule action='drop' direction='in'>
    <tcp state='NONE' flags='SYN/ALL'/>
</rule>

* docs/internals.html.in: Fix xml errors.
* docs/formatstorageencryption.html.in: Likewise.
* docs/drvesx.html.in: Likewise.
* docs/archnetwork.html.in: Likewise.
* docs/logging.html.in: Likewise.
* docs/drvvmware.html.in: Likewise.
* docs/api.html.in: Likewise.
* docs/formatnwfilter.html.in: Likewise.
* docs/formatdomain.html.in: Likewise.
* docs/windows.html.in: Likewise.

Fix this which went into documentation

This patch adds the possibility to not just drop packets, but to also have them rejected where iptables at least sends an ICMP msg back to the originator. On ebtables this again maps into dropping packets since rejecting is not supported.

I am adding 'since 0.8.9' to the docs assuming this will be the next version of libvirt.

This patch adds another example to the nwfilter html page and provides 2 solutions for how to write a filter meeting the given requirements using newly added features.

I am adding a row with information about the newly supported state
attribute to each of the tables describing supported attributes of protocols.

I am adding a row with information about the newly supported comment
attribute to each of the tables describing supported attributes of protocols.

As requested, here a couple of paragraphs about the recently added statematch attribute and some advanced (and tricky) traffic filtering topics.

A build on Ubuntu reported:

|| Generating formatnwfilter.html.tmp
/dados/develop/libvirt/docs/formatnwfilter.html.in|390| HTML parser error : Unexpected end tag : p
||     </p>
||         ^
/dados/develop/libvirt/docs/formatnwfilter.html.in|705| HTML parser error : Unexpected end tag : code
||          <td>End of range of valid source ports</code></td>
||                                                       ^
/dados/develop/libvirt/docs/formatnwfilter.html.in|710| HTML parser error : Unexpected end tag : code
||          <td>Start of range of valid destination ports</code></td>
||                                                              ^

* docs/formatnwfilter.html.in: Fix invalid HTML constructs.
Reported by Eduardo Otubo.

This patch adds documentation of the nwfilter subsystem of libvirt to
the existing (web) docs.