Revert "net: set SK_MEM_QUANTUM to 4096"

This reverts commit bd68a2a8.

This change broke memcg on arches with PAGE_SIZE != 4096

Later, commit 2bb2f5fb ("net: add new socket option SO_RESERVE_MEM")
also assumed PAGE_SIZE==SK_MEM_QUANTUM

Following patches in the series will greatly reduce the over allocations
problem.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/sock.h

@@ -1532,25 +1532,15 @@ int __sk_mem_schedule(struct sock *sk, int size, int kind);
 void __sk_mem_reduce_allocated(struct sock *sk, int amount);
 void __sk_mem_reclaim(struct sock *sk, int amount);
 
-/* We used to have PAGE_SIZE here, but systems with 64KB pages
- * do not necessarily have 16x time more memory than 4KB ones.
- */
-#define SK_MEM_QUANTUM 4096
+#define SK_MEM_QUANTUM ((int)PAGE_SIZE)
 #define SK_MEM_QUANTUM_SHIFT ilog2(SK_MEM_QUANTUM)
 #define SK_MEM_SEND	0
 #define SK_MEM_RECV	1
 
-/* sysctl_mem values are in pages, we convert them in SK_MEM_QUANTUM units */
+/* sysctl_mem values are in pages */
 static inline long sk_prot_mem_limits(const struct sock *sk, int index)
 {
-	long val = sk->sk_prot->sysctl_mem[index];
-
-#if PAGE_SIZE > SK_MEM_QUANTUM
-	val <<= PAGE_SHIFT - SK_MEM_QUANTUM_SHIFT;
-#elif PAGE_SIZE < SK_MEM_QUANTUM
-	val >>= SK_MEM_QUANTUM_SHIFT - PAGE_SHIFT;
-#endif
-	return val;
+	return sk->sk_prot->sysctl_mem[index];
 }
 
 static inline int sk_mem_pages(int amt)