octeontx2-pf: Reuse PF max mtu value

Reuse the maximum support HW MTU value that is fetch during probe.
Instead of fetching through mbox each time mtu is changed as the
value is fixed for interface.

Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241023161843.15543-4-gakula@marvell.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>