net/nfb: skip log for zero-sized Tx burst
net/nfb: skip log for zero-sized Tx burst

Zero-sized TX burst floods the log no more.

Signed-off-by: Martin Spinler <c000c989d08c98662d98f15448f11de169feb92d@cesnet.cz>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk