multicast: do not restore deleted record source filter mode to new one

There are two scenarios that we will restore deleted records. The first is
when device down and up(or unmap/remap). In this scenario the new filter
mode is same with previous one. Because we get it from in_dev->mc_list and
we do not touch it during device down and up.

The other scenario is when a new socket join a group which was just delete
and not finish sending status reports. In this scenario, we should use the
current filter mode instead of restore old one. Here are 4 cases in total.

old_socket new_socket before_fix after_fix
IN(A) IN(A) ALLOW(A) ALLOW(A)
IN(A) EX( ) TO_IN( ) TO_EX( )
EX( ) IN(A) TO_EX( ) ALLOW(A)
EX( ) EX( ) TO_EX( ) TO_EX( )

Fixes: 24803f38a5c0b (igmp: do not remove igmp souce list info when set link down)
Fixes: 1666d49e1d416 (mld: do not remove mld souce list info when set link down)
Signed-off-by: Hangbin Liu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/ipv4/igmp.c

···
 	spin_lock_bh(&im->lock);
 	if (pmc) {
 		im->interface = pmc->interface;
-		im->sfmode = pmc->sfmode;
-		if (pmc->sfmode == MCAST_INCLUDE) {
+		if (im->sfmode == MCAST_INCLUDE) {
 			im->tomb = pmc->tomb;
 			im->sources = pmc->sources;
 			for (psf = im->sources; psf; psf = psf->sf_next)

net/ipv6/mcast.c

···
 	spin_lock_bh(&im->mca_lock);
 	if (pmc) {
 		im->idev = pmc->idev;
-		im->mca_sfmode = pmc->mca_sfmode;
-		if (pmc->mca_sfmode == MCAST_INCLUDE) {
+		if (im->mca_sfmode == MCAST_INCLUDE) {
 			im->mca_tomb = pmc->mca_tomb;
 			im->mca_sources = pmc->mca_sources;
 			for (psf = im->mca_sources; psf; psf = psf->sf_next)