netfilter: don't allocate space for arp/bridge hooks unless needed

no need to define hook points if the family isn't supported.
Because we need these hooks for either nftables, arp/ebtables
or the 'call-iptables' hack we have in the bridge layer add two
new dependencies, NETFILTER_FAMILY_{ARP,BRIDGE}, and have the
users select them.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/Kconfig b/net/Kconfig
index efe930d..37ec8e6 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -182,6 +182,7 @@
 	depends on BRIDGE
 	depends on NETFILTER && INET
 	depends on NETFILTER_ADVANCED
+	select NETFILTER_FAMILY_BRIDGE
 	default m
 	---help---
 	  Enabling this option will let arptables resp. iptables see bridged