net/iavf: fix adding multicast MAC address

net/iavf: fix adding multicast MAC address

When the multicast address list is added, it will flush
previous addresses first, and then add new ones.
If the number of multicast address in the list exceeds
the upper limit, it will cause failure, then need to
roll back previous addresses. This patch fixes the issue.

Fixes: 05e4c3aff35f ("net/iavf: support multicast configuration")
Cc: stable@dpdk.org
Signed-off-by: Guinan Sun <guinanx.sun@intel.com>
Tested-by: Yuan Peng <yuan.peng@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>