MIPS: bpf: Use correct mask for VLAN_TAG case

Using VLAN_VID_MASK is not correct to get the vlan tag. Use
~VLAN_PRESENT_MASK instead and make sure it's u16 so the top 16-bits
will be removed. This will ensure that the emit_andi() code will not
treat this as a big 32-bit unsigned value.

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/7127/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/net/bpf_jit.c

@@ -1317,7 +1317,7 @@ jmp_cmp:
 			off = offsetof(struct sk_buff, vlan_tci);
 			emit_half_load(r_s0, r_skb, off, ctx);
 			if (code == (BPF_ANC | SKF_AD_VLAN_TAG))
-				emit_andi(r_A, r_s0, VLAN_VID_MASK, ctx);
+				emit_andi(r_A, r_s0, (u16)~VLAN_TAG_PRESENT, ctx);
 			else
 				emit_andi(r_A, r_s0, VLAN_TAG_PRESENT, ctx);
 			break;