libbpf: Don't use kernel-side u32 type in xsk.c

u32 is a kernel-side typedef. User-space library is supposed to use __u32.
This breaks Github's projection of libbpf. Do u32 -> __u32 fix.

Fixes: 94ff9ebb ("libbpf: Fix compatibility for kernels without need_wakeup")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20191029055953.2461336-1-andriin@fb.com

tools/lib/bpf/xsk.c

@@ -161,22 +161,22 @@ static void xsk_mmap_offsets_v1(struct xdp_mmap_offsets *off)
 	off->rx.producer = off_v1.rx.producer;
 	off->rx.consumer = off_v1.rx.consumer;
 	off->rx.desc = off_v1.rx.desc;
-	off->rx.flags = off_v1.rx.consumer + sizeof(u32);
+	off->rx.flags = off_v1.rx.consumer + sizeof(__u32);
 
 	off->tx.producer = off_v1.tx.producer;
 	off->tx.consumer = off_v1.tx.consumer;
 	off->tx.desc = off_v1.tx.desc;
-	off->tx.flags = off_v1.tx.consumer + sizeof(u32);
+	off->tx.flags = off_v1.tx.consumer + sizeof(__u32);
 
 	off->fr.producer = off_v1.fr.producer;
 	off->fr.consumer = off_v1.fr.consumer;
 	off->fr.desc = off_v1.fr.desc;
-	off->fr.flags = off_v1.fr.consumer + sizeof(u32);
+	off->fr.flags = off_v1.fr.consumer + sizeof(__u32);
 
 	off->cr.producer = off_v1.cr.producer;
 	off->cr.consumer = off_v1.cr.consumer;
 	off->cr.desc = off_v1.cr.desc;
-	off->cr.flags = off_v1.cr.consumer + sizeof(u32);
+	off->cr.flags = off_v1.cr.consumer + sizeof(__u32);
 }
 
 static int xsk_get_mmap_offsets(int fd, struct xdp_mmap_offsets *off)