MFC 289401: cxgbe(4): support for the kernel RSS option.

You need PCBGROUP and RSS in the kernel config to use this.

Note: Since RSS is not present in 10.x this is mostly a no-op and is
stubbed out by removing the #include of opt_rss.h. This is merged
primarily to reduce conflicts in future merges, however it does add a
couple of diagnostic messages related to RSS buckets vs RX queue
counts.

Discussed with: np
Sponsored by: Chelsio Communications