bpf: Add support for tracing_multi link fdinfo

bpf: Add support for tracing_multi link fdinfo

Adding tracing_multi link fdinfo support with following output:

pos:    0
flags:  02000000
mnt_id: 19
ino:    3087
link_type:      tracing_multi
link_id:        9
prog_tag:       599ba0e317244f86
prog_id:        94
attach_type:    59
cnt:    10
obj-id   btf-id  cookie  func
1        91593   8       bpf_fentry_test1+0x4/0x10
1        91595   9       bpf_fentry_test2+0x4/0x10
1        91596   7       bpf_fentry_test3+0x4/0x20
1        91597   5       bpf_fentry_test4+0x4/0x20
1        91598   4       bpf_fentry_test5+0x4/0x20
1        91599   2       bpf_fentry_test6+0x4/0x20
1        91600   3       bpf_fentry_test7+0x4/0x10
1        91601   1       bpf_fentry_test8+0x4/0x10
1        91602   10      bpf_fentry_test9+0x4/0x10
1        91594   6       bpf_fentry_test10+0x4/0x10

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260606123955.345967-17-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>