selftests/bpf: Fix an unused-but-set-variable compiler warning

When using clang to build selftests with LLVM=1 in make commandline,
I hit the following compiler warning:
  xdpxceiver.c:747:6: warning: variable 'total' set but not used [-Wunused-but-set-variable]
          u32 total = 0;
              ^

This patch fixed the issue by removing that declaration and its
assocatied unused operation.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211112204833.3579457-1-yhs@fb.com

tools/testing/selftests/bpf/xdpxceiver.c

@@ -744,7 +744,6 @@ static void receive_pkts(struct pkt_stream *pkt_stream, struct xsk_socket_info *
 	struct pkt *pkt = pkt_stream_get_next_rx_pkt(pkt_stream);
 	struct xsk_umem_info *umem = xsk->umem;
 	u32 idx_rx = 0, idx_fq = 0, rcvd, i;
-	u32 total = 0;
 	int ret;
 
 	while (pkt) {
@@ -799,7 +798,6 @@ static void receive_pkts(struct pkt_stream *pkt_stream, struct xsk_socket_info *
 
 		pthread_mutex_lock(&pacing_mutex);
 		pkts_in_flight -= rcvd;
-		total += rcvd;
 		if (pkts_in_flight < umem->num_frames)
 			pthread_cond_signal(&pacing_cond);
 		pthread_mutex_unlock(&pacing_mutex);