octeontx2-af: Set representor MTU from representee

commit 59c089d55c65eb8dfae5872a904d1cbd74e89d4a from
git@git.assembla.com:cavium/WindRiver.linux.git

This patch provides the functionality of setting MTU of the
representor when the corresponding REP MTU changes.

Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Change-Id: I276fa644d9868d777f31345ea8aa3a9799d90d52
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/120599
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>