be2net: Add description about various RSS hash types

Incorporated review comment from Eric Dumazet. Added description
about different RSS hash types which adapter is capable of.
Will add support for ETHTOOL_GRXFH and ETHTOOL_SRXFX as suggested
by Ben Hutchings in a later patch.

Signed-off-by: Padmanabh Ratnakar <padmanabh.ratnakar@emulex.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>