Don't add null port to hostname attribute on JFR events

[jasonjkeller]

Fix for https://new-relic.atlassian.net/browse/NR-345540

It appears that if the Java agent cannot obtain the port associated with a host then it will set it to null, resulting in a host.hostname attribute with a value like 4326afc46b32:null being added to JFR events (where 4326afc46b32 is the hostname and null is the port number). This seems to be causing errors with GraphQL queries related to the Flame graph.

The approach that we follow with other agent data forms is to omit the port if it is null, so this PR follows that approach rather than setting a dummy port value.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.56%. Comparing base (13ad7f1) to head (a140bb6).

Files with missing lines	Patch %	Lines
...c/main/java/com/newrelic/agent/jfr/JfrService.java	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2192      +/-   ##
============================================
- Coverage     70.58%   70.56%   -0.02%     
+ Complexity     9975     9971       -4     
============================================
  Files           842      842              
  Lines         40367    40369       +2     
  Branches       6117     6118       +1     
============================================
- Hits          28494    28488       -6     
- Misses         9096     9099       +3     
- Partials       2777     2782       +5     

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