be2net:use netdev_rss_key_fill() helper

Use netdev_rss_key_fill() helper, as it provides better support for some
bonding setups.
Rename rss_hkey local variable to rss_key to have consistent name among
drivers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Sathya Perla <sathya.perla@emulex.com>
Cc: Subbu Seetharaman <subbu.seetharaman@emulex.com>
Cc: Ajit Khaparde <ajit.khaparde@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>