Add a lock around the wificond death handler and

teardownInterfaces in WifiNl80211Manager.

Prevents a specific race condition when the wificond
service dies at the same time as the Vendor HAL (whose
death handler calls into teardownInterfaces).

No other race conditions have been observed in this file,
so we can limit the locks to these 2 methods.

Bug: 273175980
Test: atest WifiNl80211ManagerTest
Change-Id: Ib3936ed8ddb3c0dc5fb25a56e535ab27a28cfa65