Revert "flow_offload: action should not be NULL when it is referenced"

This reverts commit 9ea3e52c.

Cited commit added a check to make sure 'action' is not NULL, but
'action' is already dereferenced before the check, when calling
flow_offload_has_one_action().

Therefore, the check does not make any sense and results in a smatch
warning:

include/net/flow_offload.h:322 flow_action_mixed_hw_stats_check() warn:
variable dereferenced before check 'action' (see line 319)

Fix by reverting this commit.

Cc: gushengxian <gushengxian@yulong.com>
Fixes: 9ea3e52c

 ("flow_offload: action should not be NULL when it is referenced")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20210819105842.1315705-1-idosch@idosch.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>