net/bonding: fix slave add for mode 4

net/bonding: fix slave add for mode 4

Moved the link status validity check from the slave add to the slave
activation step. Otherwise slave add will fail for mode 4 if
the ports are all stopped but only one of them checked.

Removed activate slave call from slave add function.

Bugzilla ID: 52
Fixes: b77d21cc2364 ("ethdev: add link status get/set helper functions")
Cc: stable@dpdk.org
Signed-off-by: Radu Nicolau <radu.nicolau@intel.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>