bridge: only include nf_queue.h if needed

After merging the netfilter-next tree, today's linux-next build (powerpc
ppc44x_defconfig) failed like this:

In file included from net/bridge/br_input.c:19:
include/net/netfilter/nf_queue.h:16:23: error: field 'state' has incomplete type
  struct nf_hook_state state;
                       ^~~~~

Fixes: 971502d7 ("bridge: netfilter: unroll NF_HOOK helper in bridge input path")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/bridge/br_input.c

@@ -16,7 +16,9 @@
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/netfilter_bridge.h>
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 #include <net/netfilter/nf_queue.h>
+#endif
 #include <linux/neighbour.h>
 #include <net/arp.h>
 #include <linux/export.h>