[release-v2.0] p2p: Ban peer with mix inv when disablerelaytx is active

Version 2.0.1 of dcrd will now not send invs related to mixing when
disablerelaytx is signalled during the peer negotiation stage.
Therefore, the wallet should ban peers that incorrectly send such invs
when the wallet was configured with this flag.

While there may still be some peers running v2.0.0 (which would cause
them to be banned from the wallet), their number should be small enough
to not cause significant connection issues.

Backport of a92f57a.

p2p/peering.go

@@ -2141,13 +2141,16 @@ func (rp *RemotePeer) GetInitState(ctx context.Context, msg *wire.MsgGetInitStat
 	}
 }
 
-// invVecContainsTx returns true if at least one inv vector is of type
-// transaction.
-func invVecContainsTx(inv []*wire.InvVect) bool {
+// invVecContainsTxOrMix returns true if at least one inv vector is of type
+// transaction or mix message.
+func invVecContainsTxOrMix(inv []*wire.InvVect) bool {
 	for i := range inv {
 		if inv[i].Type == wire.InvTypeTx {
 			return true
 		}
+		if inv[i].Type == wire.InvTypeMix {
+			return true
+		}
 	}
 	return false
 }
@@ -2157,7 +2160,7 @@ func (rp *RemotePeer) receivedInv(ctx context.Context, inv *wire.MsgInv) {
 	const opf = "remotepeer(%v).receivedInv"
 
 	// When tx relay is disabled, we don't expect transactions on invs.
-	if rp.lp.disableRelayTx && invVecContainsTx(inv.InvList) {
+	if rp.lp.disableRelayTx && invVecContainsTxOrMix(inv.InvList) {
 		op := errors.Opf(opf, rp.raddr)
 		err := errors.E(op, errors.Protocol, "received tx in msginv when tx relaying is disabled")
 		rp.Disconnect(err)