Bluetooth: Introduce custom APIs for L2cap socket for Obex over L2cap

Introduce custom APIs for the L2CAP socket for the obex over l2cap
feature.

The applications which uses obex over L2cap feature can make use
of these APIs to create L2cap socket.

CRs-Fixed: 639499
Change-Id: I423ae95ec4e1dc02712609e7c25d2274c5816149