ot-br-posix: Add dep to ipset as used by firewall

ipset is used by firewall module of ot-br-posix:

third_party/openthread/repo/src/posix/platform/firewall.cpp:
return ExecuteCommand("%s add %s %s -exist", kIpsetCommand, aSetName, aAddress);

Related observed issue looked like:

oniro@oniro-linux-blueprint-gateway-raspberrypi4-64:~$ sudo journalctl -u otbr-agent.service
Apr 28 17:42:32 oniro-linux-blueprint-gateway-raspberrypi4-64 systemd[1]: Started OpenThread Border Router Agent.
Apr 28 17:42:38 oniro-linux-blueprint-gateway-raspberrypi4-64 otbr-agent[330]: sh: ipset: not found

Relate-to: eclipse/oniro-blueprints/transparent-gateway/meta-oniro-blueprints-gateway#6 Cc: Stefan Schmidt stefan.schmidt@huawei.com Origin: https://github.com/openembedded/meta-openembedded/pull/611 Forwarded: https://gitlab.eclipse.org/eclipse/oniro-core/oniro/-/merge_requests?author_username=pcoval&scope=all&state=all Signed-off-by: Philippe Coval philippe.coval.ext@huawei.com

meta-oniro-core/recipes-connectivity/openthread/ot-br-posix_git.bbappend

@@ -6,3 +6,5 @@ inherit writables
 
 WRITABLES = "data"
 WRITABLE_PATH[data] = "/var/lib/thread/"
+
+RDEPENDS:${PN} += "ipset"