optimize: do not print stateful information

optimize: do not print stateful information

Do not print stateful information such as counters which are likely set
to zero.

Before this patch:

  Merging:
  packets.conf:10:3-29:                 ip protocol  4 counter drop
  packets.conf:11:3-29:                 ip protocol 41 counter drop
  packets.conf:12:3-29:                 ip protocol 47 counter drop
  into:
          ip protocol { 4, 41, 47 } counter packets 0 bytes 0 drop
                                            ^^^^^^^^^^^^^^^^^
After:

  Merging:
  packets.conf:10:3-29:                 ip protocol  4 counter drop
  packets.conf:11:3-29:                 ip protocol 41 counter drop
  packets.conf:12:3-29:                 ip protocol 47 counter drop
  into:
          ip protocol { 4, 41, 47 } counter drop

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>