bpf: improve handling of various sizes of BPF_MAP_CREATE attributes

bpf: improve handling of various sizes of BPF_MAP_CREATE attributes

* bpf.c (BEGIN_BPF_CMD_DECODER(BPF_MAP_CREATE)): Skip printing
the rest of the structure if len is less than the offset of the end
of max_entries, map_flags, or inner_map_fd field.
* tests/bpf.c (BPF_MAP_CREATE_checks): Add two more checks.