rpm: Add fields to *.service and *.socket files

[imanti]

Add missing rules in file lldpad.service:

• Requires=lldpad.socket # Bring up socket when service goes up
• Restart=always # Attempt to start service when is down

and missing information in file lldpad.socket:

• Add [Unit] section with description of socket

[praeluceo]

FYI this PR is in our validation lab, however I do not expect any progress until after the Thanksgiving holiday. That said, I don't see any reason why we can't just merge this PR, so I'm pinging @dmertman to see if we can just pull this one in, it's been a frustrating nuance of the service since the beginning.