sfxge(4): sync tlv_layout.h with firmwaresrc and update port-mode definition use

It fixes driver attach issue to a new firmware which reports a new
port-modes.

Reviewed by: gnn
Submitted by: Tom Millington <tmillington at solarflare.com>
Sponsored by: Solarflare Communications, Inc.
MFC after: 2 days
Differential Revision: https://reviews.freebsd.org/D8203