for a port. Fix other related issues while here:
- Require port lock for access to link_config.
- Allow 100Mbps operation by tracking the speed in Mbps. Yes, really.
- New port flag to indicate that the media list is immutable. It will
be used in future refinements.
This also fixes a bug where the driver reports incorrect media with
recent firmwares.
MFC after: 2 days
Sponsored by: Chelsio Communications