ethdev: do nothing if all-multicast mode is applied again

ethdev: do nothing if all-multicast mode is applied again

Since driver callbacks return status code now, there is no necessity
to enable or disable all-multicast mode once again if it is already
successfully enabled or disabled.

Configuration restore at startup tries to ensure that configured
all-multicast mode is applied and start will return error if it fails.

Also it avoids theoretical cases when already configured all-multicast
mode is applied once again and fails. In this cases it is unclear
which value should be reported on get (configured or opposite).

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>