unexport sock_map_fd(), switch to sock_alloc_file()

Both modular callers of sock_map_fd() had been buggy; sctp one leaks
descriptor and file if copy_to_user() fails, 9p one shouldn't be
exposing file in the descriptor table at all.

Switch both to sock_alloc_file(), export it, unexport sock_map_fd() and
make it static.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/net.h b/include/linux/net.h
index 99276c3..c8a9708 100644
--- a/include/linux/net.h
+++ b/include/linux/net.h
@@ -65,6 +65,7 @@
 struct poll_table_struct;
 struct pipe_inode_info;
 struct inode;
+struct file;
 struct net;
 
 #define SOCK_ASYNC_NOSPACE	0
@@ -246,7 +247,7 @@
 				  size_t len);
 extern int	     sock_recvmsg(struct socket *sock, struct msghdr *msg,
 				  size_t size, int flags);
-extern int 	     sock_map_fd(struct socket *sock, int flags);
+extern struct file  *sock_alloc_file(struct socket *sock, int flags);
 extern struct socket *sockfd_lookup(int fd, int *err);
 extern struct socket *sock_from_file(struct file *file, int *err);
 #define		     sockfd_put(sock) fput(sock->file)