eth: fbnic: Add message parsing for FW messages

Add FW message formatting and parsing. The TLV format should
look very familiar to those familiar with netlink.
Since we don't have to deal with backward compatibility
we tweaked the format a little to make it easier to deal
with, and more appropriate for tightly coupled interfaces
like driver<>FW communication.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Link: https://patch.msgid.link/172079936754.1778861.1029830244010564007.stgit@ahduyck-xeon-server.home.arpa


Signed-off-by: Jakub Kicinski <kuba@kernel.org>