LE: Remove general/limited discoverability bits for non-connectable adv

According to the Bluetooth spec, section 9.1.1.2, "A device in the
broadcast mode shall not set the ‘LE General Discoverable Mode’
flag or the ‘LE Limited Discoverable Mode’ flag in the Flags AD Type.

This patch masks out the specific bits for non-connectable
advertisements.

Bug: 16924631
Change-Id: Ia2c0011fb31de3e4166a8bd2c2732e50aad3a610