Merge branch 'bpf-btf-for-htab-lru'

Yonghong Song says:

====================
Commit a26ca7c9 ("bpf: btf: Add pretty print support to
the basic arraymap") added pretty print support to array map.
This patch adds pretty print for hash and lru_hash maps.

The following example shows the pretty-print result of a pinned
hashmap. Without this patch set, user will get an error instead.

    struct map_value {
            int count_a;
            int count_b;
    };

    cat /sys/fs/bpf/pinned_hash_map:

    87907: {87907,87908}
    57354: {37354,57355}
    76625: {76625,76626}
    ...

Patch #1 fixed a bug in bpffs map_seq_next() function so that
all elements in the hash table will be traversed.
Patch #2 implemented map_seq_show_elem() and map_check_btf()
callback functions for hash and lru hash maps.
Patch #3 enhanced tools/testing/selftests/bpf/test_btf.c to
test bpffs hash and lru hash map pretty print.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>