bpf, net: sock_map memory usage

sockmap and sockhash don't have something in common in allocation, so let's
introduce different helpers to calculate their memory usage.

The reuslt as follows,

- before
28: sockmap  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B
29: sockhash  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B

- after
28: sockmap  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524608B
29: sockhash  name count_map  flags 0x0  <<<< no updated elements
        key 4B  value 4B  max_entries 65536  memlock 1048896B

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-16-laoar.shao@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>