net: add sanity check in proto_register()

prot->memory_allocated should only be set if prot->sysctl_mem
is also set.

This is a followup of commit 25206111 ("crypto: af_alg - get
rid of alg_memory_allocated").
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20220216171801.3604366-1-eric.dumazet@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/sock.c

@@ -3718,6 +3718,10 @@ int proto_register(struct proto *prot, int alloc_slab)
 {
 	int ret = -ENOBUFS;
 
+	if (prot->memory_allocated && !prot->sysctl_mem) {
+		pr_err("%s: missing sysctl_mem\n", prot->name);
+		return -EINVAL;
+	}
 	if (alloc_slab) {
 		prot->slab = kmem_cache_create_usercopy(prot->name,
 					prot->obj_size, 0,