bridge: only provide proxy ARP when CONFIG_INET is enabled

When IPV4 support is disabled, we cannot call arp_send from
the bridge code, which would result in a kernel link error:

net/built-in.o: In function `br_handle_frame_finish':
:(.text+0x59914): undefined reference to `arp_send'
:(.text+0x59a50): undefined reference to `arp_tbl'

This makes the newly added proxy ARP support in the bridge
code depend on the CONFIG_INET symbol and lets the compiler
optimize the code out to avoid the link error.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 958501163ddd ("bridge: Add support for IEEE 802.11 Proxy ARP")
Cc: Kyeyoon Park <kyeyoonp@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_input.c

@@ -154,7 +154,8 @@ int br_handle_frame_finish(struct sk_buff *skb)
 	dst = NULL;
 
 	if (is_broadcast_ether_addr(dest)) {
-		if (p->flags & BR_PROXYARP &&
+		if (IS_ENABLED(CONFIG_INET) &&
+		    p->flags & BR_PROXYARP &&
 		    skb->protocol == htons(ETH_P_ARP))
 			br_do_proxy_arp(skb, br, vid);