Add user_agent for ip_address.
Each [class@GSSDP.Client] maintains a mapping of addresses (MAC on systems that support it, IP addresses otherwise) to User Agents.
This information can be used in higher layers to get an User-Agent for devices that do not set the User-Agent header in their SOAP requests.
| this |
A Client |
| ip_address |
The host to add to the cache |
| user_agent |
User agent ot the host to add |