[EBTABLES]: Move more stuff into ebt_verify_pointers().

Take intialization of ->hook_entry[...], ->entries_size and ->nentries
over there, pull the check for empty chains into the end of that sucker.

Now it's self-contained, so we can move it up in the very beginning of
translate_table() *and* we can rely on ->hook_entry[] being properly
transliterated after it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>