octeontx2-pf: cn10k: Get max mtu supported from admin function

CN10K supports max MTU of 16K on LMAC links and 64k on LBK
links and Octeontx2 silicon supports 9K mtu on both links.
Get the same from nix_get_hw_info mbox message in netdev probe.

This patch also calculates receive buffer size required based
on the MTU set.

Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>