MFC r267912, r267915:
- Exclude loopback address rather than loopback interface.
- style(9)

Spotted by:	melifaro
MFC r267955 and r268209:
- Add proper rangechecks in "axge_rx_frame()" function and
fix receive loop header parsing.
- Disable hardware checksumming until it is properly tested.

PR:		191432