gsocks5proxy: Fix SOCKS5 username/password authentication
It was checking for the main SOCKS5 version number, rather than the subnegotiation version number. The username/password authentication protocol is described in https://tools.ietf.org/html/rfc1929.
Spotted and diagnosed by lovetox.
Signed-off-by: Philip Withnall withnall@endlessm.com
Fixes: #1986 (closed)