router: Remove useless mutex lock in TCP handler
router: Remove useless mutex lock in TCP handler

A new route is built each time Set is called, and wrapping a go call
in a mutex lock makes no sense in this case.

Closes #1034

Signed-off-by: Jonathan Rudenberg <3692bfa45759a67d83aedf0045f6cb635a966abf@titanous.com>

lmars/flynn,lmars/flynn,philiplb/flynn,philiplb/flynn,philiplb/flynn,flynn/flynn,philiplb/flynn,flynn/flynn,flynn/flynn,flynn/flynn,lmars/flynn,lmars/flynn,flynn/flynn,philiplb/flynn,lmars/flynn