net: remove NET_LL_RX_POLL config menue

Remove NET_LL_RX_POLL from the config menu.
Change default to y.
Busy polling still needs to be enabled at run time.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>