net-sysfs: use rps_tag_ptr and remove metadata from rps_sock_flow_table

net-sysfs: use rps_tag_ptr and remove metadata from rps_sock_flow_table

Instead of storing the @mask at the beginning of rps_sock_flow_table,
use 5 low order bits of the rps_tag_ptr to store the log of the size.

This removes a potential cache line miss to fetch @mask.

More importantly, we can switch to vmalloc_huge() without wasting memory.

Tested with:

numactl --interleave=all bash -c "echo 4194304 >/proc/sys/net/core/rps_sock_flow_entries"

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260302181432.1836150-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>