cxgbe: Implement tcp_info handler for connections handled by t4_tom.

The TCB is read using a memory window right now. A better alternate to
get self-consistent, uncached information would be to use a GET_TCB
request but waiting for a reply from hw while holding non-sleepable
locks is quite inconvenient.

Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D14817