Bluetooth: ISO: Allow binding a PA sync socket

This makes it possible to bind a PA sync socket to a number of BISes
before issuing the BIG Create Sync command.

Signed-off-by: Iulia Tanasescu <iulia.tanasescu@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>