ipmr/ip6mr: allow to get unresolved cache via netlink

/proc/net/ip[6]_mr_cache allows to get all mfc entries, even if they are put in
the unresolved list (mfc[6]_unres_queue). But only the table RT_TABLE_DEFAULT is
displayed.
This patch adds the parsing of the unresolved list when the dump is made via
rtnetlink, hence each table can be checked.

In IPv6, we set rtm_type in ip6mr_fill_mroute(), because in case of unresolved
mfc __ip6mr_fill_mroute() will not set it. In IPv4, it is already done.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>