ip_input: remove pointless check in INP_RECVIF handling

An mbuf rcvif pointer is supposed to be valid and doesn't
need extra checks.  The code appeared in d314ad7b.

sys/netinet/ip_input.c

@@ -1281,8 +1281,7 @@ ip_savecontrol(struct inpcb *inp, struct mbuf **mp, struct ip *ip,
 		struct sockaddr_dl *sdp;
 		struct sockaddr_dl *sdl2 = &sdlbuf.sdl;
 
-		if ((ifp = m->m_pkthdr.rcvif) &&
-		    ifp->if_index && ifp->if_index <= V_if_index) {
+		if ((ifp = m->m_pkthdr.rcvif)) {
 			sdp = (struct sockaddr_dl *)ifp->if_addr->ifa_addr;
 			/*
 			 * Change our mind and don't try copy.