ixgbe: Fix incomplete speed coverage in link status logging

Originally ixgbe_if_update_admin_status() only handled 1G and 10G speeds,
causing any other speeds to display as "1 Gbps" in link status logs.

This issue is fixed by adding link speed to string conversion logic through
the introduction of a helper function, ixgbe_link_speed_to_str(), which
corrects the misleading logs to reflect accurate link speeds.

Signed-off-by: Yogesh Bhosale yogesh.bhosale@intel.com

PR: 288960
Reported by: Mike Belanger - QNX
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D52442