Add support for single --sport and --dport parsing

Previously if someone already had a rule with a single --sport or --dport we
would fail the parse. This now accepts parsing in the single variant, while
still supporting the multiport variant.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'ticket/master/single_sport_dport_support_for_parsing'

* ticket/master/single_sport_dport_support_for_parsing:
  Add support for single --sport and --dport parsing