This change makes Dial, Listen and ListenPacket with invalid port fail
whatever GODEBUG=netdns is.

Please be informed that cgoLookupPort with an out of range literal
number may return either the lower or upper bound value, 0 or 65535,
with no error on some platform.

Fixes #11715.

Change-Id: I43f9c4fb5526d1bf50b97698e0eb39d29fd74c35
Reviewed-on: https://go-review.googlesource.com/12447Reviewed-by: Ian Lance Taylor <iant@golang.org>