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>