bpf: fix building without CONFIG_INET

The newly added TCP and UDP handling fails to link when CONFIG_INET
is disabled:

net/core/filter.o: In function `sk_lookup':
filter.c:(.text+0x7ff8): undefined reference to `tcp_hashinfo'
filter.c:(.text+0x7ffc): undefined reference to `tcp_hashinfo'
filter.c:(.text+0x8020): undefined reference to `__inet_lookup_established'
filter.c:(.text+0x8058): undefined reference to `__inet_lookup_listener'
filter.c:(.text+0x8068): undefined reference to `udp_table'
filter.c:(.text+0x8070): undefined reference to `udp_table'
filter.c:(.text+0x808c): undefined reference to `__udp4_lib_lookup'
net/core/filter.o: In function `bpf_sk_release':
filter.c:(.text+0x82e8): undefined reference to `sock_gen_put'

Wrap the related sections of code in #ifdefs for the config option.

Furthermore, sk_lookup() should always have been marked 'static', this
also avoids a warning about a missing prototype when building with
'make W=1'.

Fixes: 6acc9b4 ("bpf: Add helper to retrieve socket in BPF")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Joe Stringer <joe@wand.net.nz>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

net/core/filter.c

@@ -4817,8 +4817,9 @@ static const struct bpf_func_proto bpf_lwt_seg6_adjust_srh_proto = {
 };
 #endif /* CONFIG_IPV6_SEG6_BPF */
 
-struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
-		       struct sk_buff *skb, u8 family, u8 proto)
+#ifdef CONFIG_INET
+static struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
+			      struct sk_buff *skb, u8 family, u8 proto)
 {
 	int dif = skb->dev->ifindex;
 	bool refcounted = false;
@@ -4951,6 +4952,7 @@ static const struct bpf_func_proto bpf_sk_release_proto = {
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_SOCKET,
 };
+#endif /* CONFIG_INET */
 
 bool bpf_helper_changes_pkt_data(void *func)
 {
@@ -5158,12 +5160,14 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 	case BPF_FUNC_skb_ancestor_cgroup_id:
 		return &bpf_skb_ancestor_cgroup_id_proto;
 #endif
+#ifdef CONFIG_INET
 	case BPF_FUNC_sk_lookup_tcp:
 		return &bpf_sk_lookup_tcp_proto;
 	case BPF_FUNC_sk_lookup_udp:
 		return &bpf_sk_lookup_udp_proto;
 	case BPF_FUNC_sk_release:
 		return &bpf_sk_release_proto;
+#endif
 	default:
 		return bpf_base_func_proto(func_id);
 	}
@@ -5264,12 +5268,14 @@ sk_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_sk_redirect_hash_proto;
 	case BPF_FUNC_get_local_storage:
 		return &bpf_get_local_storage_proto;
+#ifdef CONFIG_INET
 	case BPF_FUNC_sk_lookup_tcp:
 		return &bpf_sk_lookup_tcp_proto;
 	case BPF_FUNC_sk_lookup_udp:
 		return &bpf_sk_lookup_udp_proto;
 	case BPF_FUNC_sk_release:
 		return &bpf_sk_release_proto;
+#endif
 	default:
 		return bpf_base_func_proto(func_id);
 	}