xtensa: ISS: always use fixed tuntap config

The code doesn't handle dynamic TAP interface allocation, so there's no
point tracking this case.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: ISS: raise network polling rate to 10 times/sec

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: ISS: clean up diagnostic, increase verbosity

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>