tty: n_gsm: depends on NET

n_gsm uses skb functions, so it should depend on NET.

n_gsm.c:(.text+0x123d49): undefined reference to `skb_dequeue'
n_gsm.c:(.text+0x123d98): undefined reference to `kfree_skb'
n_gsm.c:(.text+0x123e1e): undefined reference to `skb_pull'
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/char/Kconfig

@@ -284,6 +284,7 @@ config N_HDLC
 config N_GSM
 	tristate "GSM MUX line discipline support (EXPERIMENTAL)"
 	depends on EXPERIMENTAL
+	depends on NET
 	help
 	  This line discipline provides support for the GSM MUX protocol and
 	  presents the mux as a set of 61 individual tty devices.