net/mlx5: fix link status query

net/mlx5: fix link status query

Trying to query the link status through the new ETHTOOL_GLINKSETTINGS
ioctl available since Linux 4.5 was always failing due to a kernel bug
fixed since version 4.9.

This commit also addresses a common issue where the headers version used
at compile time differs from that of the kernel on the target system, by
always defining missing symbols and moving the kernel version check at run
time.

Fixes: 188408719888 ("net/mlx5: fix support for newer link speeds")
CC: stable@dpdk.org
Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
Acked-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>