provide arg to error

BEFORE:

```
E[05-24|11:55:37.229] Dialing failed                               pex=0 addr=022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593 err="Connect to self: <nil>" attempts=0
```

AFTER:

```
E[05-24|11:55:37.229] Dialing failed                               pex=0 addr=022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593 err="Connect to self: 022ec801d79025caab3afbbf816d92ff8450d040@127.0.0.2:6593" attempts=0
```

p2p/switch.go

@@ -568,7 +568,7 @@ func (sw *Switch) addPeer(pc peerConn) error {
 		// and add to our addresses to avoid dialing again
 		sw.addrBook.RemoveAddress(addr)
 		sw.addrBook.AddOurAddress(addr)
-		return ErrSwitchConnectToSelf{}
+		return ErrSwitchConnectToSelf{addr}
 	}
 
 	// Avoid duplicate

p2p/switch_test.go

@@ -193,7 +193,7 @@ func TestSwitchFiltersOutItself(t *testing.T) {
 	// addr should be rejected in addPeer based on the same ID
 	err := s1.DialPeerWithAddress(rp.Addr(), false)
 	if assert.Error(t, err) {
-		assert.EqualValues(t, ErrSwitchConnectToSelf{}, err)
+		assert.Equal(t, ErrSwitchConnectToSelf{rp.Addr()}.Error(), err.Error())
 	}
 
 	assert.True(t, s1.addrBook.OurAddress(rp.Addr()))