windows: support Windows SOCKADDR_BTH structure
windows: support Windows SOCKADDR_BTH structure

Implements the Windows SOCKADDR_BTH structure so
it can be used as a parameter in windows.Connect.

Fixes: golang/go#53929
Change-Id: Ibe54071897b60ecd91f44c7c0c894d831e56fe56
Reviewed-on: https://go-review.googlesource.com/c/sys/+/419394
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Auto-Submit: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@google.com>
Reviewed-by: Alex Brainman <54ba58c8441b5eff861de6b4e5ee46baf086b142@gmail.com>

golang/sys,golang/sys,golang/sys