net: ipv4: fix compilation warning for uninitialized variable

It is possible that the 'in' variable is used without
initialization. This change fixes uninitialized variable usage.

Change-Id: If26733110b29ec1c1150f1da50efa0c1ac6c2796
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>