ipv4: constify ip_mc_sf_allow() socket argument

This clarifies ip_mc_sf_allow() intent.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/igmp.h

@@ -122,7 +122,7 @@ extern int ip_mc_msfget(struct sock *sk, struct ip_msfilter *msf,
 			sockptr_t optval, sockptr_t optlen);
 extern int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 			sockptr_t optval, size_t offset);
-extern int ip_mc_sf_allow(struct sock *sk, __be32 local, __be32 rmt,
+extern int ip_mc_sf_allow(const struct sock *sk, __be32 local, __be32 rmt,
 			  int dif, int sdif);
 extern void ip_mc_init_dev(struct in_device *);
 extern void ip_mc_destroy_dev(struct in_device *);

net/ipv4/igmp.c

@@ -2638,10 +2638,10 @@ int ip_mc_gsfget(struct sock *sk, struct group_filter *gsf,
 /*
  * check if a multicast source filter allows delivery for a given <src,dst,intf>
  */
-int ip_mc_sf_allow(struct sock *sk, __be32 loc_addr, __be32 rmt_addr,
+int ip_mc_sf_allow(const struct sock *sk, __be32 loc_addr, __be32 rmt_addr,
 		   int dif, int sdif)
 {
-	struct inet_sock *inet = inet_sk(sk);
+	const struct inet_sock *inet = inet_sk(sk);
 	struct ip_mc_socklist *pmc;
 	struct ip_sf_socklist *psl;
 	int i;