fixup! Add no_hmac_verify flag

Commit a62b7c9b was broken in that
2 nodes with same id/hmac settings could not communicate when
1 of the 2 has no_hmac_verify.

hmac.c

@@ -259,6 +259,7 @@ check_hmac(const unsigned char *packet, int packetlen, int bodylen,
 {
     int i = bodylen + 4;
     int len;
+    int rc = -1;
 
     debugf("check_hmac %s -> %s\n",
 	   format_address(src), format_address(dst));
@@ -278,8 +279,9 @@ check_hmac(const unsigned char *packet, int packetlen, int bodylen,
                               packet + i + 2, len, ifp->key);
 	    if(ok)
 		return 1;
+	    rc = 0;
 	}
 	i += len + 2;
     }
-    return 0;
+    return rc;
 }

message.c

@@ -580,21 +580,24 @@ parse_packet(const unsigned char *from, struct interface *ifp,
         bodylen = packetlen - 4;
     }
 
-    if(ifp->key != NULL && !(ifp->flags & IF_NO_HMAC_VERIFY)) {
-        if(check_hmac(packet, packetlen, bodylen, from, to, ifp) != 1) {
-            fprintf(stderr, "Received wrong hmac.\n");
-            return;
-        }
-
-        neigh = find_neighbour(from, ifp);
-        if(neigh == NULL) {
-            fprintf(stderr, "Couldn't allocate neighbour.\n");
-            return;
-        }
-
-        if(preparse_packet(packet, bodylen, neigh, ifp) == 0) {
-            fprintf(stderr, "Received wrong PC or failed the challenge.\n");
-            return;
+    if(ifp->key != NULL) {
+        switch(check_hmac(packet, packetlen, bodylen, from, to, ifp)) {
+            case -1:
+                if(ifp->flags & IF_NO_HMAC_VERIFY)
+                    break; /* missing key ignored */
+            case 0:
+                fprintf(stderr, "Received wrong hmac.\n");
+                return;
+            case 1:
+                neigh = find_neighbour(from, ifp);
+                if(neigh == NULL) {
+                    fprintf(stderr, "Couldn't allocate neighbour.\n");
+                    return;
+                }
+                if(preparse_packet(packet, bodylen, neigh, ifp) == 0) {
+                    fprintf(stderr, "Received wrong PC or failed the challenge.\n");
+                    return;
+                }
         }
     }