iavf: fix potential races for FDIR filters

Add fdir_fltr_lock locking in unprotected places.

The change in iavf_fdir_is_dup_fltr adds a spinlock around a loop which
iterates over all filters and looks for a duplicate. The filter can be
removed from list and freed from memory at the same time it's being
compared. All other places where filters are deleted are already
protected with spinlock.

The remaining changes protect adapter->fdir_active_fltr variable so now
all its uses are under a spinlock.

Fixes: 527691bf

 ("iavf: Support IPv4 Flow Director filters")
Signed-off-by: Piotr Gardocki <piotrx.gardocki@intel.com>
Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230807205011.3129224-1-anthony.l.nguyen@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>