export broadcast receiver in BlockedNumberActivity

This commit adds the exported flag for the receivers registered
for BLOCK_SUPPRESSION_STATE_CHANGED
BLOCK_SUPPRESSION_STATE_CHANGED is sent by the BlockedNumberProvider.

Fixes: 274915661
Fixes: 272947672
Test: m Telecom, manual test
Change-Id: I0dbf312439e44caa501711784fde8fc45dba9a2b