Fix CEF processor mapping exception (elastic#17220)

Extensions spriv/dpriv were mapped to {source|destination}.user.group
instead of {source|destination}.user.group.name.

This caused a mapping exception when attempting to ingest CEF logs that
used those extensions.

Fixes elastic#17216

(cherry picked from commit 99f483e)

CHANGELOG.next.asciidoc

@@ -129,6 +129,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Fix Elasticsearch `_id` field set by S3 and Google Pub/Sub inputs. {pull}17026[17026]
 - Fixed various Cisco FTD parsing issues. {issue}16863[16863] {pull}16889[16889]
 - Fix default index pattern in IBM MQ filebeat dashboard. {pull}17146[17146]
+- Fixed a mapping exception when ingesting CEF logs that used the spriv or dpriv extensions. {issue}17216[17216] {pull}17220[17220]
 
 *Heartbeat*
 

x-pack/filebeat/module/cef/log/test/cef.log

@@ -1,2 +1,3 @@
 CEF:0|Elastic|Vaporware|1.0.0-alpha|18|Web request|low|eventId=3457 requestMethod=POST slat=38.915 slong=-77.511 proto=TCP sourceServiceName=httpd requestContext=https://www.google.com src=6.7.8.9 spt=33876 dst=192.168.10.1 dpt=443 request=https://www.example.com/cart
 CEF:0|Elastic|Vaporware|1.0.0-alpha|18|Authentication|low|eventId=123 src=6.7.8.9 spt=33876 dst=1.2.3.4 dpt=443 duser=alice suser=bob destinationTranslatedAddress=10.10.10.10 fileHash=bc8bbe52f041fd17318f08a0f73762ce oldFileHash=a9796280592f86b74b27e370662d41eb
+CEF:0|Elastic|Vaporware|1.0.0-alpha|18|Authentication|low|spriv=user dpriv=root

x-pack/filebeat/module/cef/log/test/cef.log-expected.json

@@ -121,5 +121,34 @@
         "tags": [
             "cef"
         ]
+    },
+    {
+        "cef.device.event_class_id": "18",
+        "cef.device.product": "Vaporware",
+        "cef.device.vendor": "Elastic",
+        "cef.device.version": "1.0.0-alpha",
+        "cef.extensions.destinationUserPrivileges": "root",
+        "cef.extensions.sourceUserPrivileges": "user",
+        "cef.name": "Authentication",
+        "cef.severity": "low",
+        "cef.version": "0",
+        "destination.user.group.name": "root",
+        "event.code": "18",
+        "event.dataset": "cef.log",
+        "event.module": "cef",
+        "event.original": "CEF:0|Elastic|Vaporware|1.0.0-alpha|18|Authentication|low|spriv=user dpriv=root",
+        "event.severity": 0,
+        "fileset.name": "log",
+        "input.type": "log",
+        "log.offset": 531,
+        "message": "Authentication",
+        "observer.product": "Vaporware",
+        "observer.vendor": "Elastic",
+        "observer.version": "1.0.0-alpha",
+        "service.type": "cef",
+        "source.user.group.name": "user",
+        "tags": [
+            "cef"
+        ]
     }
 ]

x-pack/filebeat/processors/decode_cef/keys.ecs.go

@@ -45,7 +45,7 @@ var ecsExtensionMapping = map[string]mappedField{
 	"destinationTranslatedPort":    {Target: "destination.nat.port"},
 	"destinationUserId":            {Target: "destination.user.id"},
 	"destinationUserName":          {Target: "destination.user.name"},
-	"destinationUserPrivileges":    {Target: "destination.user.group"},
+	"destinationUserPrivileges":    {Target: "destination.user.group.name"},
 	"deviceAction":                 {Target: "event.action"},
 	"deviceAddress":                {Target: "observer.ip"},
 	"deviceDirection": {
@@ -108,7 +108,7 @@ var ecsExtensionMapping = map[string]mappedField{
 	"sourceTranslatedPort":    {Target: "source.nat.port"},
 	"sourceUserId":            {Target: "source.user.id"},
 	"sourceUserName":          {Target: "source.user.name"},
-	"sourceUserPrivileges":    {Target: "source.user.group"},
+	"sourceUserPrivileges":    {Target: "source.user.group.name"},
 	"startTime":               {Target: "event.start"},
 	"transportProtocol": {
 		Target: "network.transport",