server: bind to IPv4 localhost by default

server: bind to IPv4 localhost by default

Since OpenOCD basically allows to perform arbitrary actions on behalf of
the running user, it makes sense to restrict the exposure by default.

If you need network connectivity and your environment is safe enough,
use "bindto 0.0.0.0" to switch to the old behaviour.

Change-Id: I4a4044b90d0ecb30118cea96fc92a7bcff0924e0
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/4331
Reviewed-by: Jonathan McDowell <noodles-openocd@earth.li>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins