bpf: Invert the dependency between bpf-netns.h and netns/bpf.h

netns/bpf.h gets included by netdevice.h (thru net_namespace.h)
which in turn gets included in a lot of places. We should keep
netns/bpf.h as light-weight as possible.

bpf-netns.h seems to contain more implementation details than
deserves to be included in a netns header. It needs to pull in
uapi/bpf.h to get various enum types.

Move enum netns_bpf_attach_type to netns/bpf.h and invert the
dependency. This makes netns/bpf.h fit the mold of a struct
definition header more clearly, and drops the number of objects
rebuilt when uapi/bpf.h is touched from 7.7k to 1.1k.

Signed-off-by: Jakub Kicinski <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

include/linux/bpf-netns.h

···
 #define _BPF_NETNS_H
 
 #include <linux/mutex.h>
+#include <net/netns/bpf.h>
 #include <uapi/linux/bpf.h>
-
-enum netns_bpf_attach_type {
-	NETNS_BPF_INVALID = -1,
-	NETNS_BPF_FLOW_DISSECTOR = 0,
-	NETNS_BPF_SK_LOOKUP,
-	MAX_NETNS_BPF_ATTACH_TYPE
-};
 
 static inline enum netns_bpf_attach_type
 to_netns_bpf_attach_type(enum bpf_attach_type attach_type)

include/net/netns/bpf.h

···
 #ifndef __NETNS_BPF_H__
 #define __NETNS_BPF_H__
 
-#include <linux/bpf-netns.h>
+#include <linux/list.h>
 
 struct bpf_prog;
 struct bpf_prog_array;
+
+enum netns_bpf_attach_type {
+	NETNS_BPF_INVALID = -1,
+	NETNS_BPF_FLOW_DISSECTOR = 0,
+	NETNS_BPF_SK_LOOKUP,
+	MAX_NETNS_BPF_ATTACH_TYPE
+};
 
 struct netns_bpf {
 	/* Array of programs to run compiled from progs or links */