Makes http::serve take a SockAddr instead of a starting

[sr-gi]

This is a pretty simple PR, but it was hurting my eyes seeing that much replication and weird variable naming with respect to the internal API.

In a nutshell, this simply makes http::serve take grpc_bind as SocketAddr instead of String, so we can get rid of a useless variable and rename things more accordingly.

[sr-gi]

Actually, we only needed to enclose once (i.e. we don't need to clone twice, the second, and last, time can be a move).

[sr-gi]

@mariocynicys can you re-ack if this makes sense?

[sr-gi]

Removed the latest commit