[MEDIUM] frontend: check for LI_O_TCP_RULES in the listener

[MEDIUM] frontend: check for LI_O_TCP_RULES in the listener

The new LI_O_TCP_RULES listener option indicates that some TCP rules
must be checked upon accept on this listener. It is now checked by
the frontend and the L4 rules are evaluated only in this case. The
flag is only set when at least one tcp-req rule is present in the
frontend.

The L4 rules check function has now been moved to proto_tcp.c where
it ought to be.