Changed NET_PORT_CHECK to REQ_NET_PORT_CHECK, to improve consistency

I originally made this change because I needed the OPT_NET_PORT_CHECK,
and I am committing it even if I don't need anymore OPT_NET_PORT_CHECK
because IMO it improves the consistency of the name of the wrappers.

Also, I changed the code of the check to use inequality operators
chaining.

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>