net/mlx5: fix assert in modify converting

net/mlx5: fix assert in modify converting

The assertion was added incorrectly in converting the modify actions
into the format of low layer driver.
There is no mask specified in the rte_flow actions, and PMD driver
will give a mask of all 1s to the field to be modified. For each
field, the mask could not be zero. But for the whole header which
contains this field, the masks of other fields could be zero. The
assertion needs to be removed for debug mode.

Fixes: 72a944dba163 ("net/mlx5: fix header modify action validation")
Cc: stable@dpdk.org
Signed-off-by: Bing Zhao <bingz@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>