Fixed race condition in handling available networks list

When modem reports back to back available networks list, we
should batch process them.

Test: Unit tests + manual
Bug: 132113909
Merged-In: I0071ae6812bbc698a41ba1a303971032a84f2034
Change-Id: I0071ae6812bbc698a41ba1a303971032a84f2034
(cherry picked from commit eecee44c)