net: rename rtnl_net_debug to lock_debug

And make it selected by CONFIG_DEBUG_NET. Don't rename any of
the structs/functions. Next patch will use rtnl_net_debug_event in
netdevsim.

Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250401163452.622454-5-sdf@fomichev.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Stanislav Fomichev

net/core/Makefile

@@ -45,5 +45,5 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_sk_storage.o
 obj-$(CONFIG_OF)	+= of_net.o
 obj-$(CONFIG_NET_TEST) += net_test.o
 obj-$(CONFIG_NET_DEVMEM) += devmem.o
-obj-$(CONFIG_DEBUG_NET_SMALL_RTNL) += rtnl_net_debug.o
+obj-$(CONFIG_DEBUG_NET) += lock_debug.o
 obj-$(CONFIG_FAIL_SKB_REALLOC) += skb_fault_injection.o