ipmr_cache_find
c = ipmr_cache_find(mrt, sr->src.s_addr, sr->grp.s_addr);
c = ipmr_cache_find(mrt, sr.src.s_addr, sr.grp.s_addr);
cache = ipmr_cache_find(mrt, ip_hdr(skb)->saddr, ip_hdr(skb)->daddr);
cache = ipmr_cache_find(mrt, ip_hdr(skb)->saddr, ip_hdr(skb)->daddr);
cache = ipmr_cache_find(mrt, saddr, daddr);
cache = ipmr_cache_find(mrt, src, grp);