set LocalAddr in outbound gateway conns

This means that the IP you dial from is the same IP that you listen on. As a consequence, when you manually bind to an IP, as in:

siad --rpc-addr 123.456.789.0:1234

peers that you connect to will see your RemoteAddr as 123.456.789.0.

This should (hopefully) fix #1970 (closed). I'm not sure how to test it though; the best confirmation would be for @D4rk4 or another contributor with this sort of networking setup to test that it works for them.