Add a Test for NattKeepalive Unsupported on WLAN

Adds a test that verifies that NATT Keepalive requests
are rejected on WLAN while passed on WWAN.

Bug: 72417084
Test: runtest -x DataConnectionTest.java
Merged-In: I710cd8c47a712aec7211cfd026610bb7449743d8
Change-Id: I710cd8c47a712aec7211cfd026610bb7449743d8
(cherry picked from commit 8e990e5f)