Fix Windows tun setup crash

Fix Windows tun setup crash

The intention was to use vpninfo->hostname, by passing it as a parameter
to the create_ifname_w() function. But that function still just uses
vpninfo->ifname unconditionally, ignoring the argument. And causing the
crash in #370.

Fix up some bogus formatting while we're at it. We don't do open braces
on the same line as the function declaration.

Fixes: 48bd28aadd ("Use hostname as Wintun ifname (if ifname not specified)")
Signed-off-by: David Woodhouse <dwmw2@infradead.org>