Fixups; default to :http for ListenAndServe, remove unused vars

[aviddiviner]

Just some small fixups:

• ListenAndServeTLS allocated addr but never used it.
• ListenAndServe didn't default to listen on :http like it should.

[aviddiviner]

I also added TCP keep-alives on connections from ListenAndServe. As you can see from the docs on net/http:

ListenAndServe listens on the TCP network address srv.Addr and then calls Serve to handle requests on incoming connections. Accepted connections are configured to enable TCP keep-alives.

Keep-alives were already being done on ListenAndServeTLS.