Use pts flag to create broadcast without encryption

Allow to start broadcast without encrytion.

To enable it use:
PTS_BroadcastUnencrypted=true

Bug: 238151156
Test: atest BluetoothInstrumentationTests
Tag: #feature

Merged-In: Ie7aff67cdca7f25008237f5f50e89502ab81ab77
Change-Id: Ie7aff67cdca7f25008237f5f50e89502ab81ab77
(cherry picked from commit 5508eee1)