MIPS: bpf: Fix return values for VLAN_TAG_PRESENT case

If VLAN_TAG_PRESENT is not zero, then return 1 as expected by
classic BPF. Otherwise return 0.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: netdev@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7128/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/net/bpf_jit.c

@@ -1316,10 +1316,13 @@ static int build_body(struct jit_ctx *ctx)
 						  vlan_tci) != 2);
 			off = offsetof(struct sk_buff, vlan_tci);
 			emit_half_load(r_s0, r_skb, off, ctx);
-			if (code == (BPF_ANC | SKF_AD_VLAN_TAG))
+			if (code == (BPF_ANC | SKF_AD_VLAN_TAG)) {
 				emit_andi(r_A, r_s0, (u16)~VLAN_TAG_PRESENT, ctx);
-			else
+			} else {
 				emit_andi(r_A, r_s0, VLAN_TAG_PRESENT, ctx);
+				/* return 1 if present */
+				emit_sltu(r_A, r_zero, r_A, ctx);
+			}
 			break;
 		case BPF_ANC | SKF_AD_PKTTYPE:
 			ctx->flags |= SEEN_SKB;