handle OSError if port not present in /etc/services

[pUrGe12]

Proposed change

A shorter version of PR #1074. This is to handle unknown ports inside /etc/services, instead of not reporting that port as running, nettacker can call it "unknown"

Type of change

• New core framework functionality
• Bugfix (non-breaking change which fixes an issue)
• Code refactoring without any functionality changes
• New or existing module/payload change
• Documentation/localization improvement
• Test coverage improvement
• Dependency upgrade
• Other improvement (best practice, cleanup, optimization, etc)

Checklist

• I've followed the contributing guidelines
• I've run make pre-commit, it didn't generate any changes
• I've run make test, all tests passed locally

[arkid15r]

LGTM