net/i40e: fix disabling flex payload selection rule

net/i40e: fix disabling flex payload selection rule

When setting up the flexible paylaod selection rules, the value
NONUSE_FLX_PIT_DEST_OFF (== 63) is meant to disable the rule.
However, since the MK_FLX_PIT macro always added on an additional
offset of I40E_FLX_OFFSET_IN_FIELD_VECTOR (== 50) to the value passed
the functionality to disable the rule was broken.
This patch fixes this by checking for the disable value and not adding
the offset in that case.

Fixes: d8b90c4eabe9 ("i40e: take flow director flexible payload configuration")

Reported-by: Michael Habibi <mikehabibi@gmail.com>
Signed-off-by: Jingjing Wu <jingjing.wu@intel.com>
Acked-by: Zhe Tao <zhe.tao@intel.com>