bpf: bpf_struct_ops memory usage

bpf: bpf_struct_ops memory usage

A new helper is introduced to calculate bpf_struct_ops memory usage.

The result as follows,

- before
1: struct_ops  name count_map  flags 0x0
        key 4B  value 256B  max_entries 1  memlock 4096B
        btf_id 73

- after
1: struct_ops  name count_map  flags 0x0
        key 4B  value 256B  max_entries 1  memlock 5016B
        btf_id 73

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-13-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>