[IPV6]: The ifa lock is a BH lock

The ifa lock is expected to be taken in BH context (by addrconf timers)
so we must disable BH when accessing it from user context.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -1909,11 +1909,11 @@ static int inet6_addr_add(int ifindex, struct in6_addr *pfx, int plen,
 	ifp = ipv6_add_addr(idev, pfx, plen, scope, ifa_flags);
 
 	if (!IS_ERR(ifp)) {
-		spin_lock(&ifp->lock);
+		spin_lock_bh(&ifp->lock);
 		ifp->valid_lft = valid_lft;
 		ifp->prefered_lft = prefered_lft;
 		ifp->tstamp = jiffies;
-		spin_unlock(&ifp->lock);
+		spin_unlock_bh(&ifp->lock);
 
 		addrconf_dad_start(ifp, 0);
 		in6_ifa_put(ifp);