net: use WSASocket instead of socket call

net: use WSASocket instead of socket call

WSASocket (unlike socket call) allows to create sockets that
will not be inherited by child process. So call WSASocket to
save on using syscall.ForkLock and calling syscall.CloseOnExec.

Some very old versions of Windows do not have that functionality.
Call socket, if WSASocket failed, to support these.

Change-Id: I2dab9fa00d1a8609dd6feae1c9cc31d4e55b8cb5
Reviewed-on: https://go-review.googlesource.com/72590
Reviewed-by: Ian Lance Taylor <iant@golang.org>