doc/netlink: Fix typos in operation attributes

doc/netlink: Fix typos in operation attributes

I'm trying to generate Rust bindings for netlink using the yaml spec.

It looks like there's a typo in conntrack spec: attribute set conntrack-attrs
defines attributes "counters-{orig,reply}" (plural), while get operation
references "counter-{orig,reply}" (singular). The latter should be fixed, as it
denotes multiple counters (packet and byte). The corresonding C define is
CTA_COUNTERS_ORIG.

Also, dump request references "nfgen-family" attribute, which neither exists in
conntrack-attrs attrset nor ctattr_type enum. There's member of nfgenmsg struct
with the same name, which is where family value is actually taken from.

> static int ctnetlink_dump_exp_ct(struct net *net, struct sock *ctnl,
>                struct sk_buff *skb,
>                const struct nlmsghdr *nlh,
>                const struct nlattr * const cda[],
>                struct netlink_ext_ack *extack)
> {
>   int err;
>   struct nfgenmsg *nfmsg = nlmsg_data(nlh);
>   u_int8_t u3 = nfmsg->nfgen_family;
                         ^^^^^^^^^^^^

Signed-off-by: Remy D. Farley <one-d-wide@protonmail.com>
Fixes: 23fc9311a526 ("netlink: specs: add conntrack dump and stats dump support")
Link: https://patch.msgid.link/20250913140515.1132886-1-one-d-wide@protonmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>