MFC r352982:
Add support for buffer parameter manipulations in mlx5en(4).
The following sysctls are added:
dev.mce.N.conf.qos.cable_length
dev.mce.N.conf.qos.buffers_size
dev.mce.N.conf.qos.buffers_prio
Submitted by: kib@
Sponsored by: Mellanox Technologies