octeontx2-af: Fix key checking for source mac

Given a field with its location/offset in input packet,
the key checking logic verifies whether extracting the
field can be supported or not based on the mkex profile
loaded in hardware. This logic is wrong wrt source mac
and this patch fixes that.

Fixes: 9b179a96 ("octeontx2-af: Generate key field bit mask from KEX profile")
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>