Add Prefix per Carrier requirement

Some carrier requires if users dial an emergency number address with
some prefix, the combination of the prefix and the address is also a
valid emergency number to dial.

Bug: 122429213
Test: Treehugger
Change-Id: Ib9b96bb0a210aba64a8652984d22f3564813fa9d
Merged-In: Ib9b96bb0a210aba64a8652984d22f3564813fa9d
(cherry picked from commit 69f48c5e)