mlx5en: Set ifmr_current same as ifmr_active.

This both:

• makes ifconfig media line similar to that of other drivers.
• fixes ENXIO in case when paradoxical current media word is not registered.

Now e.g.

ifconfig mce0 -mediaopt txpause,rxpause

works by disabling pauses if enabled.

Sponsored by: Mellanox Technologies/NVidia Networking
MFC after: 1 week