IB/ipoib: Update broadcast object if PKey value was changed in index 0

Update the broadcast address in the priv->broadcast object when the
Pkey value changes in index 0, otherwise the multicast GID value will
keep the previous value of the PKey, and will not be updated.
This leads to interface state down because the interface will keep the
old PKey value.

For example, in SR-IOV environment, if the PF changes the value of PKey
index 0 for one of the VFs, then the VF receives PKey change event that
triggers heavy flush. This flush calls update_parent_pkey that update the
broadcast object and its relevant members. If in this case the multicast
GID will not be updated, the interface state will be down.

Fixes: c2904141 ("IPoIB: Fix pkey change flow for virtualization environments")
Signed-off-by: Feras Daoud <ferasda@mellanox.com>
Signed-off-by: Erez Shitrit <erezsh@mellanox.com>
Reviewed-by: Alex Vesker <valex@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>