Speed up remote bitbang.

Speed up remote bitbang.

1. Use TCP_NODELAY, which makes things twice as fast.
2. Get rid of a bunch of unnecessary socket block/non-block calls, which
improves speed another 10% or so.

Change-Id: I415db5746d55374a14564b1973b81e3517f5cb67
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6534
Tested-by: jenkins
Reviewed-by: Jan Matyas <matyas@codasip.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>