bnxt_en: Improve multicast address setup logic.

The driver builds a list of multicast addresses and sends it to the
firmware when the driver's ndo_set_rx_mode() is called.  In rare
cases, the firmware can fail this call if internal resources to
add multicast addresses are exhausted.  In that case, we should
try the call again by setting the ALL_MCAST flag which is more
guaranteed to succeed.

Fixes: c0c050c5

 ("bnxt_en: New Broadcom ethernet driver.")
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>