Fix issue with pulling a previously pulled call.

The bug reported is that sometimes a call isn't marked as pullable when
it should be.
The mExternalCallPullableState map tracks the last pullable state reported
by the network.  When a new external call is created, there was an issue
where the network pullable state was not being correctly tracked.  Further
updates to the network pullable state were not saved.

Bug: 30047706
Change-Id: I37060f12c393f2e2aba2bd2e8e3237f152495807