kni: fix crash with null name

kni: fix crash with null name

Fix a segmentation fault which occurs when the kni_autotest is run
in the 'test' application.

This segmenation fault occurs when rte_kni_get() is called with a
NULL value for 'name'.

Fixes: 0c6bc8ef70ba ("kni: memzone pool for alloc and release")
Cc: stable@dpdk.org
Signed-off-by: Dan Gora <dg@adax.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>