proxy protocol: improve logging

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

internal/common/common.go

@@ -831,6 +831,8 @@ func getProxyPolicy(allowed, skipped []func(net.IP) bool, def proxyproto.Policy)
 		}
 
 		if def == proxyproto.REQUIRE {
+			logger.Debug(logSender, "", "reject connection from ip %q: proxy protocol signature required and not set",
+				upstreamIP)
 			return proxyproto.REJECT, proxyproto.ErrInvalidUpstream
 		}
 		return def, nil