feat(healthcheck/icmp): use the same id and increasing sequence number

- easier debug logs flow
- MAY cost less conntrack-ed slots on the VPN server
- resets id and sequence to 1 when reconnecting VPN
- resets id and sequence to 1 after 5 minutes
- resets id and sequence to 1 if sequence is complete (65535)

internal/healthcheck/checker.go

@@ -74,6 +74,7 @@ func (c *Checker) Start(ctx context.Context) (runError <-chan error, err error)
 		// restore forced check type to dns if icmp was found to be not permitted
 		c.smallCheckType = smallCheckDNS
 	}
+	c.echoer.Reset()
 
 	err = c.startupCheck(ctx)
 	if err != nil {