netfilter: Move NATTYPE forward mode to POSTROUTING chain.

When UL data path is through IPA, only one packet traverses
through SW. NATTYPE module requires at least 2 packets to create
a valid NATTYPE entry. As the NATTYPE entry is not created, DL
data fails in ARCN and FCN. Move NATTYPE forward mode to
POSTROUTING chain to create the NATTYPE entry with only one packet.

Change-Id: Ic03436339e2b0a6c4277146942f518e6c7d49574
Signed-off-by: Ravinder Konka <rkonka@codeaurora.org>