Bluetooth: bnep: bnep_add_connection() should verify that it's dealing with l2cap socket

commit 71bb99a02b32b4cc4265118e85f6035ca72923f0 upstream.

same story as cmtp

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>