Bluetooth: Add missing selection of CONFIG_CRC16 for L2CAP layer

Fix net/bluetooth/l2cap.c build errors:

l2cap.c:(.text+0x126035): undefined reference to `crc16'
l2cap.c:(.text+0x126323): undefined reference to `crc16'
l2cap.c:(.text+0x12668e): undefined reference to `crc16'
l2cap.c:(.text+0x12683b): undefined reference to `crc16'
l2cap.c:(.text+0x126956): undefined reference to `crc16'
net/built-in.o:l2cap.c:(.text+0x129041): more undefined references to `crc16' follow
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/bluetooth/Kconfig

@@ -34,6 +34,7 @@ menuconfig BT
 config BT_L2CAP
 	tristate "L2CAP protocol support"
 	depends on BT
+	select CRC16
 	help
 	  L2CAP (Logical Link Control and Adaptation Protocol) provides
 	  connection oriented and connection-less data transport.  L2CAP