[IPV6]: Fix modular build with netfilter enabled.

Also, drop __exit marker from ipv6_netfilter_fini() as this
can be invoked from inet6_init() error handling paths.

Based upon a report from Stephen Hemminger.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/Makefile b/net/ipv6/Makefile
index bf18cff..41877ab 100644
--- a/net/ipv6/Makefile
+++ b/net/ipv6/Makefile
@@ -12,13 +12,14 @@
 
 ipv6-$(CONFIG_XFRM) += xfrm6_policy.o xfrm6_state.o xfrm6_input.o \
 	xfrm6_output.o
+ipv6-$(CONFIG_NETFILTER) += netfilter.o
 ipv6-objs += $(ipv6-y)
 
 obj-$(CONFIG_INET6_AH) += ah6.o
 obj-$(CONFIG_INET6_ESP) += esp6.o
 obj-$(CONFIG_INET6_IPCOMP) += ipcomp6.o
 obj-$(CONFIG_INET6_TUNNEL) += xfrm6_tunnel.o 
-obj-$(CONFIG_NETFILTER)	+= netfilter.o netfilter/
+obj-$(CONFIG_NETFILTER)	+= netfilter/
 
 obj-$(CONFIG_IPV6_TUNNEL) += ip6_tunnel.o