nfp: remove unused suspicious mask defines

NFP_NET_RXR_MASK sounds like a mask which could be used on
NFP_NET_CFG_RXRS_ENABLE register but its value is quite
strange.  In fact there are no users of this define so let's
just remove it.  Same for TX rings.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>