bpf: libbpf: Provide basic API support to specify BPF obj name

bpf: libbpf: Provide basic API support to specify BPF obj name

This patch extends the libbpf to provide API support to
allow specifying BPF object name.

In tools/lib/bpf/libbpf, the C symbol of the function
and the map is used.  Regarding section name, all maps are
under the same section named "maps".  Hence, section name
is not a good choice for map's name.  To be consistent with
map, bpf_prog also follows and uses its function symbol as
the prog's name.

This patch adds logic to collect function's symbols in libbpf.
There is existing codes to collect the map's symbols and no change
is needed.

The bpf_load_program_name() and bpf_map_create_name() are
added to take the name argument.  For the other bpf_map_create_xxx()
variants, a name argument is directly added to them.

In samples/bpf, bpf_load.c in particular, the symbol is also
used as the map's name and the map symbols has already been
collected in the existing code.  For bpf_prog, bpf_load.c does
not collect the function symbol name.  We can consider to collect
them later if there is a need to continue supporting the bpf_load.c.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>