extensions: libipt_realm: add a missing space in translation

extensions: libipt_realm: add a missing space in translation

We missed a blank space when do translate to nft, so if rt_realm can be
mapped to name, the result looks ugly:
  # iptables-translate -A OUTPUT -m realm --realm 0
  nft add rule ip filter OUTPUT rtclassidcosmos counter
                                         ^

Apply this patch:
  # iptables-translate -A OUTPUT -m realm --realm 0
  nft add rule ip filter OUTPUT rtclassid cosmos counter

Signed-off-by: Liping Zhang <liping.zhang@spreadtrum.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>