net/i40e: cache flow director enable value in Rx queue

net/i40e: cache flow director enable value in Rx queue

This commit adds a fdir_enable flag in a uint8_t sized hole
the rx queue structure The flag enables the rx code path to
easily identify if fdir is active. This can be used to skip
fdir id processing when it is not required.

The flag is zero by default (as rxq is zmalloc-ed at startup),
and the flag is set to 1 on configuration of a flow director rule.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>
Tested-by: Mesut Ali Ergin <mesut.a.ergin@intel.com>