net/i40e: optimize flow director memory management

net/i40e: optimize flow director memory management

This patch allocated some memory pool for flow management to avoid
calling rte_zmalloc/rte_free every time.
This patch also improves the hash table operation. When adding/removing
a flow, the software will directly add/delete it from the hash table.
If any error occurs, it then roll back the operation it just done.

Signed-off-by: Chenmin Sun <chenmin.sun@intel.com>
Reviewed-by: Jingjing Wu <jingjing.wu@intel.com>