macvlan: don't touch promisc without passthrough

commit df8ef8f3
"macvlan: add FDB bridge ops and macvlan flags"
added a way to control NOPROMISC macvlan flag through netlink.

However, with a non passthrough device we never set promisc on open,
even if NOPROMISC is off.  As a result:

If userspace clears NOPROMISC on open, then does not clear it on a
netlink command, promisc counter is not decremented on stop and there
will be no way to clear it once macvlan is detached.

If userspace does not clear NOPROMISC on open, then sets NOPROMISC on a
netlink command, promisc counter will be decremented from 0 and overflow
to fffffffff with no way to clear promisc.

To fix, simply ignore NOPROMISC flag in a netlink command for
non-passthrough devices, same as we do at open/close.

Since we touch this code anyway - check dev_set_promiscuity return code
and pass it to users (though an error here is unlikely).

Cc: "David S. Miller" <davem@davemloft.net>
Reviewed-by: John Fastabend <john.r.fastabend@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>