xtensa: ISS: drop IP setup, clean up MAC setup

Without proper MAC setup network device doesn't work. IP setup is
redundant and may be done with 'ip=...' kernel parameter.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
xtensa: ISS: enable iss_net_set_mac

This allows changing MAC address of the device.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
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>
xtensa: ISS: avoid simple_strtoul use

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