iptables/libiptc perf issue: Sorting chain during pull-out

iptables/libiptc perf issue: Sorting chain during pull-out

Performance optimize scalability issue:
  Sorting chain during pull-out give worst-case runtime O(Chains2).

When pulling out the blob, every chain name is inserted alphabetically
into a linked list (by function iptc_insert_chain()).  The problem
with this approach is that the chain names delivered in the blob is
already sorted (as we push it back to the kernel sorted).

This cause chain parsing to always process every element in the chain
list and finish with a tail add.  Causing worst-case runtime O(C2/2)
for alphabetically sorting of chains.

The patch solves this by only calling iptc_insert_chain() when
creating new chains.

Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>