Always use valid ids pointer in dec_ttl_cnt_ids_from_openflow()

Always use valid ids pointer in dec_ttl_cnt_ids_from_openflow()

Always update the ids pointer after calling ofpbuf_put()
to ensure that it is valid when accessed.

During testing a case came up where the call to ofpbuf_put() in the
for (i = 0; i < ids->n_controllers; i++) loop would cause the underlying
buffer to be reallocated. This resulted in ids->n_controllers being an
incorrect value, the loop continuing on longer than desired and finally a
segmentation fault.

Reported-by: Joe Stringer <joe@wand.net.nz>
Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Ben Pfaff <blp@nicira.com>