ipt_NATTYPE: Fix for changes in c7232c99

Some fields moved around or became hidden between 3.4 and 3.10.
Use the correct struct members.

Change-Id: I31e4c4acae30378f37bd4b8e4d7d617957a0545d
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>