cxgbe/t4_tom: Per-connection rate limiting for TCP sockets handled by
the TOE. For now this capability is always enabled in kernels with
options RATELIMIT. t4_tom will check if_capenable once the base driver
gets code to support rate limiting for any socket (TOE or not).

This was tested with iperf3 and netperf ToT as they already support
SO_MAX_PACING_RATE sockopt. There is a bug in firmwares prior to
1.16.45.0 that affects the BSD driver only and results in rate-limiting
at an incorrect rate. This will resolve by itself as soon as 1.16.45.0
or later firmware shows up in the driver.

Relnotes: Yes
Sponsored by: Chelsio Communications