linux: recognize TCP_INFO and ratelimit the warning

This ratelimits the "unsupported getsockopt level 6 optname 11"
warnings that happen all the time when watching Netflix.

Sponsored By: EPSRC
Differential Revision: https://reviews.freebsd.org/D32454

(cherry picked from commit 99f563ed76f49c541e587a2f81bc43c62c86c0e5)