WifiVendorHal: Clear local log event handler

Ensure that we reset the stored local handler objects even if the HAL
methods fails or if the HAL object is invalid.

Note: This is already what we do for stopRssiMonitoring().

Bug: 122062525
Bug: 114766171
Test: Verified that we're able to turn of wifi HAL logging after
toggling wifi state.
Test: ./frameworks/opt/net/wifi/tests/wifitests/runtests.sh

Change-Id: Id9fb575aacec9599a1b7576e500201009379753f
2 files changed