Ignore Reserved and DF flags in IP header

The previous code dropped DHCPv4 replies with the DF flag set in some
scenarios. This might explain the increase in provisioning failures that
we have noticed in the ApfFilter experiment launch metrics.

Test: ApfFilterTest
(cherry picked from https://android-review.googlesource.com/q/commit:a317f91d769cbf5fd3af6a83b6f00c302ad0dc28)
Merged-In: I5c38795b8b504b25fcc3bf5dc5c26b1543bea937
Change-Id: I5c38795b8b504b25fcc3bf5dc5c26b1543bea937
1 file changed