DLM must depend on IPV6 || IPV6=n

If you select something, you have to ensure that the dependencies of what you are selecting are fulfilled.

This patch fixes the following compile error with CONFIG_DLM=y and CONFIG_IPV6=m:

<-- snip -->

...
LD .tmp_vmlinux1
net/built-in.o: In function `sctp_v6_err':
ipv6.c:(.text+0x8cb67): undefined reference to icmpv6_err_convert' ipv6.c:(.text+0x8cbad): undefined reference to in6_dev_finish_destroy' ipv6.c:(.text+0x8cc4b): undefined reference to icmpv6_statistics' net/built-in.o: In function sctp_v6_xmit':
ipv6.c:(.text+0x8ccfc): undefined reference to ipv6_addr_type' ipv6.c:(.text+0x8cfca): undefined reference to ip6_xmit'
net/built-in.o: In function `sctp_v6_get_dst':
ipv6.c:(.text+0x8d031): undefined reference to ipv6_addr_type' ipv6.c:(.text+0x8d083): undefined reference to ip6_route_output' ipv6.c:(.text+0x8d4a7): undefined reference to ip6_route_output' net/built-in.o: In function sctp_v6_get_saddr':
ipv6.c:(.text+0x8d7a1): undefined reference to ipv6_get_saddr' net/built-in.o: In function sctp_v6_cmp_addr':
ipv6.c:(.text+0x8ddc0): undefined reference to ipv6_addr_type' ipv6.c:(.text+0x8de0d): undefined reference to ipv6_addr_type' ipv6.c:(.text+0x8de41): undefined reference to ipv6_addr_type' net/built-in.o: In function sctp_v6_available':
ipv6.c:(.text+0x8dee8): undefined reference to ipv6_addr_type' net/built-in.o: In function sctp_v6_addr_valid':
ipv6.c:(.text+0x8dfa2): undefined reference to ipv6_addr_type' net/built-in.o:ipv6.c:(.text+0x8e014): more undefined references to ipv6_addr_type' follow net/built-in.o: In function `sctp_v6_init':
: undefined reference to `inet6_add_protocol'
net/built-in.o: In function `sctp_v6_init':
: undefined reference to `inet6_register_protosw'
net/built-in.o: In function `sctp_v6_init':
: undefined reference to `inet6_register_protosw'
net/built-in.o: In function `sctp_v6_init':
: undefined reference to `register_inet6addr_notifier'
net/built-in.o: In function `sctp_v6_exit':
: undefined reference to `inet6_del_protocol'
net/built-in.o: In function `sctp_v6_exit':
: undefined reference to `inet6_unregister_protosw'
net/built-in.o: In function `sctp_v6_exit':
: undefined reference to `inet6_unregister_protosw'
net/built-in.o: In function `sctp_v6_exit':
: undefined reference to `unregister_inet6addr_notifier'
net/built-in.o: In function `sctp_v6_available':
ipv6.c:(.text+0x8df2a): undefined reference to ipv6_chk_addr' net/built-in.o:(.data+0x5e48): undefined reference to inet6_release' net/built-in.o:(.data+0x5e4c): undefined reference to inet6_bind' net/built-in.o:(.data+0x5e5c): undefined reference to inet6_getname' net/built-in.o:(.data+0x5e64): undefined reference to inet6_ioctl' net/built-in.o:(.data+0x5f04): undefined reference to ipv6_setsockopt' net/built-in.o:(.data+0x5f08): undefined reference to `ipv6_getsockopt'
make: *** [.tmp_vmlinux1] Error 1

<-- snip -->

@@ -3,6 +3,7 @@
 
 config DLM
 	tristate "Distributed Lock Manager (DLM)"
+	depends on IPV6 || IPV6=n
 	select IP_SCTP
 	help
 	A general purpose distributed lock manager for kernel or userspace