sunrpc: add netlink upcall for the auth.unix.ip cache

sunrpc: add netlink upcall for the auth.unix.ip cache

Add netlink-based cache upcall support for the ip_map (auth.unix.ip)
cache, using the sunrpc generic netlink family.

Add ip-map attribute-set (seqno, class, addr, domain, negative, expiry),
ip-map-reqs wrapper, and ip-map-get-reqs / ip-map-set-reqs operations
to the sunrpc_cache YAML spec and generated headers.

Implement sunrpc_nl_ip_map_get_reqs_dumpit() which snapshots pending
ip_map cache requests and sends each entry's seqno, class name, and
IP address over netlink.

Implement sunrpc_nl_ip_map_set_reqs_doit() which parses ip_map cache
responses from userspace (class, addr, expiry, and domain name or
negative flag) and updates the cache via __ip_map_lookup() /
__ip_map_update().

Wire up ip_map_notify() callback in ip_map_cache_template so cache
misses trigger SUNRPC_CMD_CACHE_NOTIFY multicast events with
SUNRPC_CACHE_TYPE_IP_MAP.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>