iptables: remove duplicated argument parsing code

1. Factor out repeated code to a new xs_has_arg function.
2. Add a new parse_wait_time option to parse the value of -w.
3. Make parse_wait_interval take argc and argv so its callers
   can be simpler.

Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(cherry picked from commit 6e2e169eb66b63d2991e1c7ada931e3cdb0ced32)

Bug: 36108349
Test: see top of change stack.
Change-Id: Iae185e267d90806dac2cbfdad2a066a2929947fc
6 files changed