Make kernel-doc support unnamed (anonymous) structs and unions.  There is
one (union) in include/linux/skbuff.h (inside struct sk_buff) that is
currently generating a kernel-doc warning, so this fixes that warning.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>