option: fix ignored negation before implicit extension loading

option: fix ignored negation before implicit extension loading

`iptables -A INPUT -p tcp ! --syn` forgot the negation, i.e. it
was not present in a subsequent `iptables -S`.

Commit v1.4.11~77^2~9 missed the fact that after autoloading a proto
extension, cs.invert must not be touched until the next getopt call.
This is now fixed by having command_default return a value to indicate
whether to jump or not.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>