Fixed dangling network agent issue

In some IWLAN handover failure cases, the associated
network agent might became dangling and causes out-of-sync
between connectivity service and telephony. Connectivity
service incorrectly thought the data connection was already
there so reaped the newly created one.

Bug: 138287040
Test: Manual
Merged-In: Idb1aa53d31f7b730946485b17fa088b97f3f9300
Change-Id: Idb1aa53d31f7b730946485b17fa088b97f3f9300
(cherry picked from commit 42e63db5)
(cherry picked from commit a5cfcb344bcfd69ad356c9c00a739525fe76f544)

CRs-fixed: 2524890
Change-Id: Idb1aa53d31f7b730946485b17fa088b97f3f9300