ethdev: add multicast address filtering

With the current PMD API, the receipt of multicast packets on a given
port can only be enabled by invoking the "rte_eth_allmulticast_enable"
function.
This method may not work on Virtual Functions in SR-IOV architectures
when the host PF driver does not allow such operation on VFs.
In such cases, joined multicast addresses must be individually added
in the set of multicast addresses that are filtered by the [VF] port.

For this purpose, a new function "set_mc_addr_list" is introduced
into the set of functions that are exported by a Poll Mode Driver.

Signed-off-by: Ivan Boule <ivan.boule@6wind.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
[Thomas: export new function in .map]
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>