Just to test, I added the full absolute path name in socketmodule.h:

#ifdef HAVE_LINUX_CAN_H
#include "/usr/include/linux/socket.h"
#include <linux/can.h>
#endif

Now, the snippet from pre-processing is:

# 182 "/usr/include/linux/tipc.h" 3 4
struct sockaddr_tipc {
 unsigned short family;
 unsigned char addrtype;
 signed char scope;
 union {
  struct tipc_portid id;
  struct tipc_name_seq nameseq;
  struct {
   struct tipc_name name;
   __u32 domain;
  } name;
 } addr;
};
# 73 "/home/vinay/projects/python/default/Modules/socketmodule.h" 2



# 1 "/usr/include/linux/socket.h" 1
# 77 "/home/vinay/projects/python/default/Modules/socketmodule.h" 2
# 1 "/usr/include/linux/can.h" 1 3 4
# 41 "/usr/include/linux/can.h" 3 4

This implies that the linux/socket.h file is not being read at all. First part of linux/socket.h is:

#ifndef _LINUX_SOCKET_H
#define _LINUX_SOCKET_H