net: sparx5: flower: only do lookup if fragment flags are set

The fragment lookup should only be performed, when
at least one of the fragment flags are set.

This change was deliberately not included in commit
68aba004 ("net: sparx5: flower: fix fragment flags handling")
as it's only needed for future proffing the code, since
"mask" is currently only set in conjunction with the
fragment flags.
(The 3rd flag FLOW_DIS_ENCAPSULATION is only used with "key")

Only compile tested.

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Reviewed-by: Daniel Machon <daniel.machon@microchip.com>
Tested-by: Daniel Machon <daniel.machon@microchip.com>
Link: https://lore.kernel.org/r/20240424121632.459022-2-ast@fiberby.net


Signed-off-by: Jakub Kicinski <kuba@kernel.org>