This patch expands on the earlier work on layer-2 mdb entries by adding
support for host entries.  Due to the fact that host joined entries do
not have any flag field, we infer the permanent flag when reporting the
entries to userspace, which otherwise would be listed as 'temp'.

Before patch:

    ~# bridge mdb add dev br0 port br0 grp 01:00:00:c0:ff:ee permanent
    Error: bridge: Flags are not allowed for host groups.
    ~# bridge mdb add dev br0 port br0 grp 01:00:00:c0:ff:ee
    Error: bridge: Only permanent L2 entries allowed.

After patch:

    ~# bridge mdb add dev br0 port br0 grp 01:00:00:c0:ff:ee permanent
    ~# bridge mdb show
    dev br0 port br0 grp 01:00:00:c0:ff:ee permanent vid 1
Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>