ethdev: more RSS flags

ethdev: more RSS flags

- i40e RSS flags have been added (and enlarged to 64-bit)
- A new configuration of 'uint8_t rss_key_len' has been added in
  'struct rte_eth_rss_conf' to support different length of RSS keys.
- In each PMD, only the supported flags are masked.

Signed-off-by: Helin Zhang <helin.zhang@intel.com>
Signed-off-by: Jing Chen <jing.d.chen@intel.com>
Acked-by: Cunming Liang <cunming.liang@intel.com>
Acked-by: Jijiang Liu <jijiang.liu@intel.com>
Acked-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Heqing Zhu <heqing.zhu@intel.com>
Tested-by: Waterman Cao <waterman.cao@intel.com>