Back out rev. 1.107 because it introduced as many problems

as it tried to solve:

- it smuggled hidden 802.1q details into otherwise protocol-neutral code;
- it put an important code consistency check under DEBUG, which was never
  defined by anyone but a developer hacking this file for the moment;
- lastly, the former bcopy() call had been correct as long as the "dead"
  code was there.

(A new version of the fix for tag of -1 to come in the next commit.)

Agreed by:	qingli

sys/net/if_vlan.c

@@ -917,15 +917,21 @@ vlan_input(struct ifnet *ifp, struct mbuf *m)
 				 __func__, ntohs(evl->evl_encap_proto)));
 
 			tag = EVL_VLANOFTAG(ntohs(evl->evl_tag));
+
+			/*
+			 * Restore the original ethertype.  We'll remove
+			 * the encapsulation after we've found the vlan
+			 * interface corresponding to the tag.
+			 */
+			evl->evl_encap_proto = evl->evl_proto;
 			break;
 		default:
-#ifdef DEBUG
-			/* XXX rate limit? */
-			if_printf(ifp, "unsupported if_type %u", ifp->if_type);
+			tag = (uint16_t) -1;
+#ifdef INVARIANTS
+			panic("%s: unsupported if_type (%u)",
+			      __func__, ifp->if_type);
 #endif
-			m_freem(m);
-			ifp->if_noproto++;	/* XXX? */
-			return;
+			break;
 		}
 	}
 
@@ -946,12 +952,12 @@ vlan_input(struct ifnet *ifp, struct mbuf *m)
 	if (mtag == NULL) {
 		/*
 		 * Packet had an in-line encapsulation header;
-		 * remove it.  Note that we leave the type field
-		 * unchanged; we only copy up the mac addresses.
+		 * remove it.  The original header has already
+		 * been fixed up above.
 		 */
 		bcopy(mtod(m, caddr_t),
 		      mtod(m, caddr_t) + ETHER_VLAN_ENCAP_LEN,
-		      ETHER_HDR_LEN - ETHER_TYPE_LEN);
+		      ETHER_HDR_LEN);
 		m_adj(m, ETHER_VLAN_ENCAP_LEN);
 	}