net: avoid possible false sharing in sk_leave_memory_pressure()

net: avoid possible false sharing in sk_leave_memory_pressure()

As mentioned in https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE#it-may-improve-performance
a C compiler can legally transform :

if (memory_pressure && *memory_pressure)
        *memory_pressure = 0;

to :

if (memory_pressure)
        *memory_pressure = 0;

Fixes: aa23fbd179ed ("tcp: add TCPMemoryPressuresChrono counter")
Fixes: 3a062d249a07 ("foundations of per-cgroup memory pressure controlling.")
Fixes: a78fd812dd9f ("[NET] CORE: Introducing new memory accounting interface.")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>