kni: reduce interface name size

The name in rte_kni_device_info is passed to the kernel, which allows
interface names with at most 16 bytes (IFNAMSIZ). rte_kni_alloc with a
longer name currently trigger a kernel BUG in alloc_netdev_mqs in
net/core/dev.c. Reduce RTE_KNI_NAMESIZE to prevent this situation.

Signed-off-by: Michael Pfeiffer <michael.pfeiffer@tu-ilmenau.de>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>