octeontx2-af: Set NIX link credits based on max LMAC

When number of LMACs active on a CGX/RPM are 3, then
current NIX link credit config based on per lmac fifo
length which inturn  is calculated as
'lmac_fifo_len = total_fifo_len / 3', is incorrect. In HW
one of the LMAC gets half of the FIFO and rest gets 1/4th.

Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Geetha Sowjanya <gakula@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>