ssh/tailssh: pass window size pixels in IoctlSetWinsize events

Fixes #13669

Change-Id: Id44cfbb83183f1bbcbdc38c29238287b9d288707
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ssh/tailssh/incubator.go

@@ -794,6 +794,8 @@ func resizeWindow(fd int, winCh <-chan ssh.Window) {
 		unix.IoctlSetWinsize(fd, syscall.TIOCSWINSZ, &unix.Winsize{
 			Row:    uint16(win.Height),
 			Col:    uint16(win.Width),
+			Xpixel: uint16(win.WidthPixels),
+			Ypixel: uint16(win.HeightPixels),
 		})
 	}
 }