tools: ynl: fix handling of multiple mcast groups

JIRA: https://issues.redhat.com/browse/RHEL-30656

commit b6c65eb20ffa8e3bd89f551427dbeee2876d72ca
Author: Jakub Kicinski <kuba@kernel.org>
Date:   Mon Feb 26 13:40:18 2024 -0800

    tools: ynl: fix handling of multiple mcast groups

    We never increment the group number iterator, so all groups
    get recorded into index 0 of the mcast_groups[] array.

    As a result YNL can only handle using the last group.
    For example using the "netdev" sample on kernel with
    page pool commands results in:

      $ ./samples/netdev
      YNL: Multicast group 'mgmt' not found

    Most families have only one multicast group, so this hasn't
    been noticed. Plus perhaps developers usually test the last
    group which would have worked.

    Fixes: 86878f14d71a ("tools: ynl: user space helpers")
    Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
    Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Link: https://lore.kernel.org/r/20240226214019.1255242-1-kuba@kernel.org
    Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Signed-off-by: Ivan Vecera <ivecera@redhat.com>

tools/net/ynl/lib/ynl.c

@@ -507,6 +507,7 @@ ynl_get_family_info_mcast(struct ynl_sock *ys, const struct nlattr *mcasts)
 				ys->mcast_groups[i].name[GENL_NAMSIZ - 1] = 0;
 			}
 		}
+		i++;
 	}
 
 	return 0;