Bluetooth: Expose L2CAP API to support OPP 1.2

Add changes to expose L2CAP API to create an insecure L2CAP socket
for supporting OPP 1.2.

Test: Connect with Remote OPP Client supporting OPP 1.2 and verify
that connection and transfer happens over L2CAP. Connect with Remote
OPP Client supporting OPP 1.1 and verify that connection and transfer
happens over RFCOMM.

Bug: 33010988
Change-Id: I21ed672afb4ed5d2355ff0a0f9691af220921c1f