peer: don't d/c peer if we encounter lnwire.ErrUnknownAddrType

In this commit, we fix a minor deviation in our implementation from the
specification. Before if we encountered an unknown error type, we would
disconnect the peer. Instead, we’ll now just continue along parsing the
remainder of the messages. This was flared up recently by some
c-lightning related incompatibilities that emerged on main net.

lnwire/lnwire.go

@@ -677,7 +677,7 @@ func readElement(r io.Reader, element interface{}) error {
 				continue
 
 			default:
-				return fmt.Errorf("unknown address type: %v", aType)
+				return ErrUnknownAddrType{aType}
 			}
 
 			addresses = append(addresses, address)