bpfilter: fix building without CONFIG_INET

bpfilter_process_sockopt is a callback that gets called from
ip_setsockopt() and ip_getsockopt(). However, when CONFIG_INET is
disabled, it never gets called at all, and assigning a function to the
callback pointer results in a link failure:

net/bpfilter/bpfilter_kern.o: In function `__stop_umh':
bpfilter_kern.c:(.text.unlikely+0x3): undefined reference to `bpfilter_process_sockopt'
net/bpfilter/bpfilter_kern.o: In function `load_umh':
bpfilter_kern.c:(.init.text+0x73): undefined reference to `bpfilter_process_sockopt'

Since there is no caller in this configuration, I assume we can
simply make the assignment conditional.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bpfilter/bpfilter_kern.c

@@ -33,7 +33,8 @@ static void shutdown_umh(struct umh_info *info)
 
 static void __stop_umh(void)
 {
-	if (bpfilter_process_sockopt) {
+	if (IS_ENABLED(CONFIG_INET) &&
+	    bpfilter_process_sockopt) {
 		bpfilter_process_sockopt = NULL;
 		shutdown_umh(&info);
 	}
@@ -98,7 +99,9 @@ static int __init load_umh(void)
 		stop_umh();
 		return -EFAULT;
 	}
+	if (IS_ENABLED(CONFIG_INET))
 		bpfilter_process_sockopt = &__bpfilter_process_sockopt;
+
 	return 0;
 }