tcp: sk_forced_mem_schedule() optimization

sk_memory_allocated_add() has three callers, and returns
to them @memory_allocated.

sk_forced_mem_schedule() is one of them, and ignores
the returned value.

Change sk_memory_allocated_add() to return void.

Change sock_reserve_memory() and __sk_mem_raise_allocated()
to call sk_memory_allocated().

This removes one cache line miss [1] for RPC workloads,
as first skbs in TCP write queue and receive queue go through
sk_forced_mem_schedule().

[1] Cache line holding tcp_memory_allocated.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>