ionic: use mc sync for multicast filters

We should be using the multicast sync routines for the multicast
filters.  Also, let's just flatten the logic a bit and pull
the small unicast routine back into ionic_set_rx_mode().

Fixes: 1800eee1 ("net: ionic: Replace in_interrupt() usage.")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>