udp: introduce __sk_mem_schedule() usage

udp: introduce __sk_mem_schedule() usage

Keep the accounting schema consistent across different protocols
with __sk_mem_schedule(). Besides, it adjusts a little bit on how
to calculate forward allocated memory compared to before. After
applied this patch, we could avoid receive path scheduling extra
amount of memory.

Link: https://lore.kernel.org/lkml/20230221110344.82818-1-kerneljasonxing@gmail.com/
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230308021153.99777-1-kerneljasonxing@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>