bonding: 3ad: allow to set ad_actor settings while the bond is up

No need to require the bond down while changing these settings, the change
will be reflected immediately and the 3ad mode will sort itself out.
For faster convergence set port->ntt to true in order to generate new
LACPDUs immediately.

CC: Jay Vosburgh <j.vosburgh@gmail.com>
CC: Veaceslav Falico <vfalico@gmail.com>
CC: Andy Gospodarek <gospo@cumulusnetworks.com>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>