kni: set default carrier state of interface

kni: set default carrier state of interface

Add module parameter 'carrier='on|off' to set the default carrier state
for linux network interfaces created by the KNI module.  The default
carrier state is 'off'.

For KNI interfaces which need to reflect the carrier state of
a physical Ethernet port controlled by the DPDK application, the
default carrier state should be left set to 'off'.  The application
can set the carrier state of the KNI interface to reflect the state
of the physical Ethernet port using rte_kni_update_link().

For KNI interfaces which are purely virtual, the default carrier
state can be set to 'on'.  This enables the KNI interface to be
used without having to explicity set the carrier state to 'on'
using rte_kni_update_link().

Signed-off-by: Dan Gora <dg@adax.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>