bpftool: Add BPF_TRACE_KPROBE_MULTI to attach type names table

BPF_TRACE_KPROBE_MULTI is a new attach type name, add it to bpftool's
table. This fixes a currently failing CI bpftool check.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220318150106.2933343-1-andrii@kernel.org