That is -- write the code, that sends diag request in new format. It's
mostly copied from tcp-diag code. Plus, sock-diag differentiates sockets
by families, thus we have to send two requests sequentially.

If we fail to submit new sock-diag request, try to fall-back and submit
the legacy tcp-diag one.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>