bpf: Fix IPv6 dport byte-order in bpf_sk_lookup

Commit 6acc9b43 ("bpf: Add helper to retrieve socket in BPF")
mistakenly passed the destination port in network byte-order to the IPv6
TCP/UDP socket lookup functions, which meant that BPF writers would need
to either manually swap the byte-order of this field or otherwise IPv6
sockets could not be located via this helper.

Fix the issue by swapping the byte-order appropriately in the helper.
This also makes the API more consistent with the IPv4 version.

Fixes: 6acc9b43 ("bpf: Add helper to retrieve socket in BPF")
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

net/core/filter.c

@@ -4721,17 +4721,18 @@ static struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
 	} else {
 		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
 		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
+		u16 hnum = ntohs(tuple->ipv6.dport);
 		int sdif = inet6_sdif(skb);
 
 		if (proto == IPPROTO_TCP)
 			sk = __inet6_lookup(net, &tcp_hashinfo, skb, 0,
 					    src6, tuple->ipv6.sport,
-					    dst6, tuple->ipv6.dport,
+					    dst6, hnum,
 					    dif, sdif, &refcounted);
 		else if (likely(ipv6_bpf_stub))
 			sk = ipv6_bpf_stub->udp6_lib_lookup(net,
 							    src6, tuple->ipv6.sport,
-							    dst6, tuple->ipv6.dport,
+							    dst6, hnum,
 							    dif, sdif,
 							    &udp_table, skb);
 #endif