BUG/MINOR: tcpchecks: fix the connect() flags regarding delayed ack

BUG/MINOR: tcpchecks: fix the connect() flags regarding delayed ack

In issue #465, we see that Coverity detected dead code in checks.c
which is in fact a missing parenthesis to build the connect() flags
consecutive to the API change in commit fdcb007ad8 ("MEDIUM: proto:
Change the prototype of the connect() method.").

The impact should be imperceptible as in the best case it may have
resulted in a missed optimization trying to save a syscall or to merge
outgoing packets.

It may be backported as far as 2.0 though it's not critical.