netfilter: fix nf_logger name in ebt_ulog.

This patch renames the ebt_ulog nf_logger from "ulog" to "ebt_ulog" to
be in sync with other modules naming. As this name was currently only
used for informational purpose, the renaming should be harmless.

Signed-off-by: Eric Leblond <eric@inl.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>