ionic: set station addr only if needed

The code was working too hard and in some cases was trying to
delete filters that weren't there, generating a potentially
misleading error message.
    IONIC_CMD_RX_FILTER_DEL (32) failed: IONIC_RC_ENOENT (-2)

Fixes: 2a654540

 ("ionic: Add Rx filter and rx_mode ndo support")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>