kni: fix large stack frame size

kni: fix large stack frame size

Compile error:
.../lib/librte_eal/linuxapp/kni/kni_net.c:
In function ‘kni_net_rx_lo_fifo’:
.../lib/librte_eal/linuxapp/kni/kni_net.c:331:1:
error: the frame size of 1056 bytes is larger than 1024 bytes
[-Werror=frame-larger-than=]

This compile error seen with some compiler / kernel combinations.

Moved some local variables to the kni_dev struct.

Fixes: 8451269e6d7b ("kni: remove continuous memory restriction")
Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>