fbnic: Move promisc_sync out of netdev code and into RPC path

fbnic: Move promisc_sync out of netdev code and into RPC path

In order for us to support the BMC possibly connecting, disconnecting, and
then reconnecting we need to be able to support entities outside of just
the NIC setting up promiscuous mode as the BMC can use a multicast
promiscuous setup.

To support that we should move the promisc_sync code out of the netdev and
into the RPC section of the driver so that it is reachable from more paths.

Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/175623748769.2246365.2130394904175851458.stgit@ahduyck-xeon-server.home.arpa
Signed-off-by: Paolo Abeni <pabeni@redhat.com>