Synchronize mRadioProxy and mOemHookProxy

We need a lock to control the write and read methods of mRadioProxy and mOemHookProxy
 to prevent race condition that may cause crashes. Making resetProxyAndRequestList
 synchronized can help with this.

Test: manual flashed the build; made a call successfully
Bug: 142333643
Change-Id: I6b0da6fe0afe0ae4db99c680518afdb6f441182f
Merged-In: I6b0da6fe0afe0ae4db99c680518afdb6f441182f
(cherry picked from commit 8f7c1195)