Restore #define's removed for unknown reason in http://git.kernel.org/cgit/linux/kernel/git/morgan/libcap.git/commit/?id=158b7732f139d12de955026074d594a8d9c84554

Without this patch libcap fails to compile with:
  cap_file.c: In function 'cap_get_fd':
  cap_file.c:190:33: error: 'XATTR_NAME_CAPS' undeclared (first use in this function)
    sizeofcaps = fgetxattr(fildes, XATTR_NAME_CAPS,
                                   ^
  cap_file.c:190:33: note: each undeclared identifier is reported only once for each function it appears in
  cap_file.c: In function 'cap_get_file':
  cap_file.c:220:34: error: 'XATTR_NAME_CAPS' undeclared (first use in this function)
    sizeofcaps = getxattr(filename, XATTR_NAME_CAPS,
                                    ^
  cap_file.c: In function 'cap_set_fd':
  cap_file.c:256:30: error: 'XATTR_NAME_CAPS' undeclared (first use in this function)
    return fremovexattr(fildes, XATTR_NAME_CAPS);
                                ^
  cap_file.c: In function 'cap_set_file':
  cap_file.c:288:31: error: 'XATTR_NAME_CAPS' undeclared (first use in this function)
    return removexattr(filename, XATTR_NAME_CAPS);
                                 ^
  make[2]: *** [cap_file.o] Error 1

--- libcap/include/uapi/linux/capability.h
+++ libcap/include/uapi/linux/capability.h
@@ -47,6 +47,8 @@
         __u32 inheritable;
 } *cap_user_data_t;
 
+#define XATTR_CAPS_SUFFIX "capability"
+#define XATTR_NAME_CAPS XATTR_SECURITY_PREFIX XATTR_CAPS_SUFFIX
 
 #define VFS_CAP_REVISION_MASK	0xFF000000
 #define VFS_CAP_REVISION_SHIFT	24