octeontx2-af: Update correct mask to filter IPv4 fragments

During the initial design, the IPv4 ip_flag mask was set to 0xff.
Which results to filter only fragmets with (fragment_offset == 0).
As part of the fix, updated the mask to 0x20 to filter all the
fragmented packets irrespective of the fragment_offset value.

Fixes: c672e372 ("octeontx2-pf: Add support to filter packet based on IP fragment")
Signed-off-by: Suman Ghosh <sumang@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>