Fix netjet driver link errors when ISDN_I4L is not enabled:

drivers/built-in.o: In function `mode_tiger':
netjet.c:(.text+0x325dc8): undefined reference to `isdnhdlc_rcv_init'
netjet.c:(.text+0x325dd5): undefined reference to `isdnhdlc_out_init'
drivers/built-in.o: In function `fill_dma':
netjet.c:(.text+0x325fb6): undefined reference to `isdnhdlc_encode'
drivers/built-in.o: In function `read_dma':
netjet.c:(.text+0x32631a): undefined reference to `isdnhdlc_decode'
drivers/built-in.o: In function `nj_irq':
netjet.c:(.text+0x326e01): undefined reference to `isdnhdlc_encode'

or move isdnhdlc.c to some other sub-dir..
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Karsten Keil <isdn@linux-pingi.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

drivers/isdn/hardware/mISDN/Kconfig

@@ -78,6 +78,7 @@ config MISDN_NETJET
 	depends on PCI
 	select MISDN_IPAC
 	select ISDN_HDLC
+	select ISDN_I4L # so that make will recurse into sub-dir.
 	help
 	  Enable support for Traverse Technologies NETJet PCI cards.