net: filter: fix SKF_AD_PKTTYPE extension on big-endian

BPF classic->internal converter broke SKF_AD_PKTTYPE extension, since
pkt_type_offset() was failing to find skb->pkt_type field which is defined as:
__u8 pkt_type:3,
     fclone:2,
     ipvs_property:1,
     peeked:1,
     nf_trace:1;

Fix it by searching for 3 most significant bits and shift them by 5 at run-time

Fixes: bd4cf0ed331a ("net: filter: rework/optimize internal BPF interpreter's instruction set")
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Tested-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/filter.c

@@ -578,7 +578,11 @@ EXPORT_SYMBOL_GPL(sk_run_filter_int_skb);
  * to make sure its still a 3bit field starting at a byte boundary;
  * taken from arch/x86/net/bpf_jit_comp.c.
  */
+#ifdef __BIG_ENDIAN_BITFIELD
+#define PKT_TYPE_MAX	(7 << 5)
+#else
 #define PKT_TYPE_MAX	7
+#endif
 static unsigned int pkt_type_offset(void)
 {
 	struct sk_buff skb_probe = { .pkt_type = ~0, };
@@ -685,6 +689,13 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
 		insn->code = BPF_ALU | BPF_AND | BPF_K;
 		insn->a_reg = A_REG;
 		insn->imm = PKT_TYPE_MAX;
+#ifdef __BIG_ENDIAN_BITFIELD
+		insn++;
+
+		insn->code = BPF_ALU | BPF_RSH | BPF_K;
+		insn->a_reg = A_REG;
+		insn->imm = 5;
+#endif
 		break;
 
 	case SKF_AD_OFF + SKF_AD_IFINDEX: