tcp: Printf should be removed.

There is a printf when a socket option down to the CC module fails, this really
should not be a printf. In fact this whole option needs to be re-thought in coordination
with some other changes in the CC modules (its just not right but its ok what it
does here if it fails since it will just use the ECN beta).

Reviewed by: Michael Tuexen
Sponsored by: Netflix Inc.
Differential Revision: https://reviews.freebsd.org/D32894