tools: ynl: add header guards for nlctrl

I "extracted" YNL C into a GitHub repo to make it easier
to use in other projects: https://github.com/linux-netdev/ynl-c

GitHub actions use Ubuntu by default, and the kernel headers
there are missing f329a0e ("genetlink: correct uAPI defines").
Add the direct include workaround for nlctrl.

Fixes: 768e044 ("doc/netlink/specs: Add spec for nlctrl netlink family")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240315002108.523232-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

tools/net/ynl/Makefile.deps

@@ -20,6 +20,7 @@ CFLAGS_ethtool:=$(call get_hdr_inc,_LINUX_ETHTOOL_NETLINK_H_,ethtool_netlink.h)
 CFLAGS_handshake:=$(call get_hdr_inc,_LINUX_HANDSHAKE_H,handshake.h)
 CFLAGS_mptcp_pm:=$(call get_hdr_inc,_LINUX_MPTCP_PM_H,mptcp_pm.h)
 CFLAGS_netdev:=$(call get_hdr_inc,_LINUX_NETDEV_H,netdev.h)
+CFLAGS_nlctrl:=$(call get_hdr_inc,__LINUX_GENERIC_NETLINK_H,genetlink.h)
 CFLAGS_nfsd:=$(call get_hdr_inc,_LINUX_NFSD_NETLINK_H,nfsd_netlink.h)
 CFLAGS_ovs_datapath:=$(call get_hdr_inc,__LINUX_OPENVSWITCH_H,openvswitch.h)
 CFLAGS_ovs_flow:=$(call get_hdr_inc,__LINUX_OPENVSWITCH_H,openvswitch.h)