[Heartbeat] Change size of data on ICMP packet (#29948)

* [Heartbeat] Change size of data on ICMP packet

* Add CHANGELOG entry.

Co-authored-by: Guillaume Marsay <[email protected]>
Co-authored-by: Justin Kambic <[email protected]>
(cherry picked from commit da9720c)

Author: 3 people

CHANGELOG.next.asciidoc

@@ -22,6 +22,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix broken macOS ICMP python e2e test. {pull}29900[29900]
 - Only add monitor.status to browser events when summary. {pull}29460[29460]
 - Also add summary to journeys for which the synthetics runner crashes. {pull}29606[29606]
+- Update size of ICMP packets to adhere to standard min size. {pull}29948[29948]
 
 *Metricbeat*
 

heartbeat/monitors/active/icmp/stdloop.go

@@ -346,7 +346,7 @@ func (l *stdICMPLoop) sendEchoRequest(addr *net.IPAddr) (*requestContext, error)
 	l.requests[id] = ctx
 	l.mutex.Unlock()
 
-	payloadBuf := make([]byte, 0, 8)
+	payloadBuf := make([]byte, 48, 48)
 	payload := bytes.NewBuffer(payloadBuf)
 	ts := time.Now()
 	binary.Write(payload, binary.BigEndian, ts.UnixNano())