[solved] [false alarm]. Bug? 100Mb instead 1Gb for lan after updating to latest snapshot

I use custom images from git source and add and remove some application via "make menuconfig"
I have always done it that way and always from git. I know it is not the most stable and I am trying to change it later but right now it is the only way I am familiar with to create custom roms.
now latest update that I installed yesterday it seems to misconfigure lan ports as 100Mb instead of 1Gb.
how do I find out what went wrong?
linux kernel maybe?

On what device/board you have that issue?

forgot to mention all that.
the router is a linksys wrt1200ac Caiman
and before this version I did not have this problem with git builds.

the fault is with my laptop I think because the odroid board conencted to router connect at 1Gb speed.

I have to check other ports.