net: fix sk_memory_allocated_{add|sub} vs softirqs

Jonathan Heathcote reported a regression caused by blamed commit
on aarch64 architecture.

x86 happens to have irq-safe __this_cpu_add_return()
and __this_cpu_sub(), but this is not generic.

I think my confusion came from "struct sock" argument,
because these helpers are called with a locked socket.
But the memory accounting is per-proto (and per-cpu after
the blamed commit). We might cleanup these helpers later
to directly accept a "struct proto *proto" argument.

Switch to this_cpu_add_return() and this_cpu_xchg()
operations, and get rid of preempt_disable()/preempt_enable() pairs.

Fast path becomes a bit faster as a result :)

Many thanks to Jonathan Heathcote for his awesome report and
investigations.

Fixes: 3cd3399d

 ("net: implement per-cpu reserves for memory_allocated")
Reported-by: Jonathan Heathcote <jonathan.heathcote@bbc.co.uk>
Closes: https://lore.kernel.org/netdev/VI1PR01MB42407D7947B2EA448F1E04EFD10D2@VI1PR01MB4240.eurprd01.prod.exchangelabs.com/
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Link: https://lore.kernel.org/r/20240421175248.1692552-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>