Silence the call when call is blocked.

Currently we won't silence the call to avoid ringing it and just wait
for the call to be disconnected. However, if the disconnection complete
after we starting ringing, user can here the ringtone for a blocked
call. Silence the call when we block it to fix this.

Bug: 292013192
Test: BlockCheckerFilterTest
Change-Id: I024159757628c13bf4f8fa434f3730d14a03c83c