ix, ixv: Update link status with autonegotiated baudrate value

Use autonegotiated link speed value while updating link status
to iflib.

This patch is part of change made in NetBSD kernel
by Masanobu Saitoh, NetBSD maintainer.

Differential Revision: https://reviews.freebsd.org/D19176
Approved by: erj

(cherry picked from commit a0302c9231502bae8f43edbd5fb8d73132eb8da7)