ns: Declare sys_setns in syscalls.h

Ooops I overlooked this one, and missing it causes compile
errors of the powerpc syscall.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

include/linux/syscalls.h

@@ -844,4 +844,5 @@ asmlinkage long sys_name_to_handle_at(int dfd, const char __user *name,
 asmlinkage long sys_open_by_handle_at(int mountdirfd,
 				      struct file_handle __user *handle,
 				      int flags);
+asmlinkage long sys_setns(int fd, int nstype);
 #endif