IPC env var and handle used by sshd is made unavailable to shell/subsystem

sshd.exe uses SSHD_REMSOC env var as private IPC for remote socket
handle passing. The env var is deleted and the handle is made not
inheritable by sshd so that shell and subsystem do not see it or have
access to the handle.

sshd.c

@@ -2809,6 +2809,10 @@ main(int ac, char **av)
         remotesochandle = atoi( getenv("SSHD_REMSOC") );
 
         sock_in = sock_out = newsock = allocate_sfd(remotesochandle) ; //si.hStdInput);
+		
+		// we have the socket handle, delete it for child processes we create like shell 
+		SetEnvironmentVariable("SSHD_REMSOC", NULL);
+		SetHandleInformation(remotesochandle, HANDLE_FLAG_INHERIT, 0); // make the handle not to be inherited
 
         /*
          * We don't have a startup_pipe