net: rtnetlink: add NLM_F_BULK support to rtnl_fdb_del

When NLM_F_BULK is specified in a fdb del message we need to handle it
differently. First since this is a new call we can strictly validate the
passed attributes, at first only ifindex and vlan are allowed as these
will be the initially supported filter attributes, any other attribute
is rejected. The mac address is no longer mandatory, but we use it
to error out in older kernels because it cannot be specified with bulk
request (the attribute is not allowed) and then we have to dispatch
the call to ndo_fdb_del_bulk if the device supports it. The del bulk
callback can do further validation of the attributes if necessary.

Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>