[PATCH net] vsock/uapi: fix linux/vm_sockets.h userspace compilation errors

[Stefano Garzarella <sgarzare@redhat.com>]

From: Stefano Garzarella <sgarzare@redhat.com>

If a userspace application just include <linux/vm_sockets.h> will fail
to build with the following errors:

    /usr/include/linux/vm_sockets.h:182:39: error: invalid application of ‘sizeof’ to incomplete type ‘struct sockaddr’
      182 |         unsigned char svm_zero[sizeof(struct sockaddr) -
          |                                       ^~~~~~
    /usr/include/linux/vm_sockets.h:183:39: error: ‘sa_family_t’ undeclared here (not in a function)
      183 |                                sizeof(sa_family_t) -
          |

Include <sys/socket.h> for userspace (guarded by ifndef __KERNEL__)
where `struct sockaddr` and `sa_family_t` are defined.
We already do something similar in <linux/mptcp.h> and <linux/if.h>.

Fixes: d021c344051a ("VSOCK: Introduce VM Sockets")
Reported-by: Daan De Meyer <daan.j.demeyer@gmail.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 include/uapi/linux/vm_sockets.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/uapi/linux/vm_sockets.h b/include/uapi/linux/vm_sockets.h
index ed07181d4eff..e05280e41522 100644
--- a/include/uapi/linux/vm_sockets.h
+++ b/include/uapi/linux/vm_sockets.h
@@ -17,6 +17,10 @@
 #ifndef _UAPI_VM_SOCKETS_H
 #define _UAPI_VM_SOCKETS_H
 
+#ifndef __KERNEL__
+#include <sys/socket.h>        /* for struct sockaddr and sa_family_t */
+#endif
+
 #include <linux/socket.h>
 #include <linux/types.h>
 
-- 
2.49.0