ethdev: advertise MTU as retained across stop/start
ethdev: advertise MTU as retained across stop/start

Changing MTU in running state may return -EBUSY saying that
MTU cannot be changed when the port is running. It assumes
that changes may be done in stopped and started (but some
PMDs may reject it) state and it is logical to require that
changes done in any of these states are retained.

Signed-off-by: Andrew Rybchenko <ac94ab2a8fe9a9a087f6e24dcbc16626b52c07e8@solarflare.com>
Acked-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk