netfilter: bridge: rename br_netfilter.c to br_netfilter_hooks.c

To prepare separation of the IPv6 code into different file.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/Makefile

@@ -12,6 +12,7 @@ bridge-$(CONFIG_SYSFS) += br_sysfs_if.o br_sysfs_br.o
 
 bridge-$(subst m,y,$(CONFIG_BRIDGE_NETFILTER)) += br_nf_core.o
 
+br_netfilter-y := br_netfilter_hooks.o
 obj-$(CONFIG_BRIDGE_NETFILTER) += br_netfilter.o
 
 bridge-$(CONFIG_BRIDGE_IGMP_SNOOPING) += br_multicast.o br_mdb.o