Bluetooth: L2CAP: Fix using wrong mode

If user has a set to use SOCK_STREAM the socket would default to
L2CAP_MODE_ERTM which later needs to be adjusted if the destination
address is LE which doesn't support such mode.

Fixes: 15f02b91

 ("Bluetooth: L2CAP: Add initial code for Enhanced Credit Based Mode")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>