msm: netfilter: changes to handle contact address modification in SIP ALG

SIP ALG mangles contact address only when both address and port are
mentioned. Some clients send only address information in which case
the contact address does not get mangled an hence SIP call does not
get established.

Change-Id: Ie760f6fcc6dd8e269b057488414b23beff4e8fc3
Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>