Regularly dump TCP_INFO statistics of outgoing connections

Backport from PR #401 to 1.7.

(cherry picked from commit b88bd91447cb143ae5a6a08ca54a9d5166314d6e)

Conflicts:
	src/libcutil.clib

Closes #401
Hmh, interesting... It was used in 1.8 before (see https://github.com/Incubaid/arakoon/blob/tcpinfo/src/msg/tcp_messaging.ml#L118) but it was removed in 8b5eb08a9173b97d6290ca2107d18dd24de8f00c for being dead code.