configure.ac: check for libnl-3 in addition to libnl-1

src/Makefile.am: link against libnl when needed

src/util/virnetlink.c:
support libnl3 api.  To minimize impact on code flow, wrap the
differences under the virNetlink* namespace.

Unfortunately libnl3 moves netlink/msg.h to
/usr/include/libnl3/netlink/msg.h, so the LIBNL_CFLAGS need to be added
to a bunch of places where they weren't needed with libnl1.
Signed-off-by: NSerge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

Some of the error messages in this function should have been
virReportSystemError (since they have an errno they want to log), but
were mistakenly written as netlinkError, which expects a libvirt error
code instead. The result was that when one of the errors was
encountered, "No error message provided" would be printed instead of
something meaningful (see
https://bugzilla.redhat.com/show_bug.cgi?id=816465 for an example).

When libvirtd is restarted, also restart the netlink event
message callbacks for existing VEPA connections and send
a message to lldpad for these existing links, so it learns
the new libvirtd pid.
Signed-off-by: ND. Herrendoerfer <d.herrendoerfer@herrendoerfer.name>

Return statements with parameter enclosed in parentheses were modified
and parentheses were removed. The whole change was scripted, here is how:

List of files was obtained using this command:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' |             \
grep -e '\.[ch]$' -e '\.py$'

Found files were modified with this command:
sed -i -e                                                                 \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'

Then checked for nonsense.

The whole command looks like this:
git grep -l -e '\<return\s*([^()]*\(([^()]*)[^()]*\)*)\s*;' |             \
grep -e '\.[ch]$' -e '\.py$' | xargs sed -i -e                            \
's_^\(.*\<return\)\s*(\(\([^()]*([^()]*)[^()]*\)*\))\s*\(;.*$\)_\1 \2\4_' \
-e 's_^\(.*\<return\)\s*(\([^()]*\))\s*\(;.*$\)_\1 \2\3_'

There are special stub versions of all public functions in this file
that are compiled when either libnl isn't available or the platform
isn't linux. Each of these functions had two almost identical message,
differing only in the function name included in the message. Since log
messages already contain the function name, we can just define a const
char* with the common part of the string, and use that same string for
all the log messages.

Also, rather than doing #if defined ... #else ... #endif *inside the
error log macro invocation*, this patch does #if defined ... just
once, using it to decide which single string to define. This turns the
error log in each function from 6 lines, to 1 line.

I'm building on OSX with no libnl. I had to do this to get src/util/virnetlink.c to compile:

Commit e3ba4025 introduced a few build errors with HAVE_LIBNL undefined.

This code adds a netlink event interface to libvirt.
It is based upon the event_poll code and makes use of
it. An event is generated for each netlink message sent
to the libvirt pid.
Signed-off-by: ND. Herrendoerfer <d.herrendoerfer@herrendoerfer.name>

Rename the src/util/netlink files to src/util/virnetlink to
better fit the naming scheme. Also rename nlComm to virNetlinkCommand.
Signed-off-by: ND. Herrendoerfer <d.herrendoerfer@herrendoerfer.name>

This patch fixes the compilation of netlink.c and interface.c on those
systems missing either libnl or that have an older linux/if_link.h
include file not supporting macvtap or VF_PORTS.

WITH_MACVTAP is '1' if newer include files were detected, '0' otherwise.

IFLA_PORT_MAX is defined in linux/if_link.h if yet more functionality is
supported.

In a first cleanup step, make nlComm from macvtap.c commonly available
for other code to use. Since nlComm uses Linux-specific structures as
parameters it's prototype is only visible on Linux.