Wrong test in func UpdateGatewayState to see if gateway coordinates should be updated

[yguel]

• The issue is present in master and 3.16.2, I do not know if master is the latest release
• I have searched the issues of this repository and believe that this is not a duplicate.

What happened?

When a gateway has an altitude of 0m, its other coordinates are not updated, even if they are not zeroes.
It looks logical from the code:
in chirpstack-network-server/internal/storage/gateway.go
around line 366

// UpdateGatewayState updates the location of the gateway and last seen ts.
func UpdateGatewayState(ctx context.Context, db sqlx.Execer, id lorawan.EUI64, lat, lon, alt float64) error {
	var loc *GPSPoint
	var altt *float64

	if lat != 0 && lon != 0 && alt != 0 {
		loc = &GPSPoint{
			Latitude:  lat,
			Longitude: lon,
		}
		altt = &alt
	}

	now := time.Now()

	// * only update first_seen_at when the current value is NULL
	// * only update the location when the given value is not NULL
	// * only update the altitude when the given value is not NULL

What did you expect?

I expect that an altitude of 0m does not prevent a gateway gps coordinates to be updated.
So I expect to have OR and not AND in the test:

if lat != 0 || lon != 0 || alt != 0 {

since I would expect that only the default coordinates (0,0,0) will cause coordinates not to be updated [poor ships cruising the Gulf of Guinea by the way ...]
And as altitude is coded as an integer (if I read correctly the packet_forwarder protocol) it might even be the case for a gateway 40cm above sea level (a buoy for instance).

Steps to reproduce this issue

Steps:

1. Make a gateway publish stats like that: {"stat":{"time":"2022-06-13 12:46:27 GMT","lati":48.5777965,"long":7.7497201,"alti":0,"rxnb":0,"rxok":0,"rxfw":0,"ackr":0,"dwnb":3,"txnb":0}}
2. gateway latitude and longitude won't be updated.

Your Environment

Component	Version
Application Server	v3.15.0
Network Server	v3.13.0
Gateway Bridge	v3.11.0
Chirpstack API
Geolocation	Not installed
Concentratord	Not installed