e1000e: add Receive Packet Steering (RPS) support

e1000e: add Receive Packet Steering (RPS) support

Enable RPS by default.  Disallow jumbo frames when both receive checksum
and receive hashing are enabled because the hardware cannot do both IP
payload checksum (enabled when receive checksum is enabled when using
packet split which is used for jumbo frames) and provide RSS hash at the
same time.

v2: added ethtool command to query flow hashing behavior per Ben Hutchings
    and changed the type of rsskey to cleanup the setting of the register
    array and avoid unnecessary casts (as pointed out by Joe Perches).
    The long error messages are not changed since there is nothing in
    the kernel ./Documentation that suggests the preferred method for
    dealing with long messages other than to never break strings; leaving
    them as-is for now.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>