bpf_glue: Remove use of bpf_load_program from libbpf

bpf_glue: Remove use of bpf_load_program from libbpf

bpf_load_program is deprecated starting in v0.7. The preferred
bpf_prog_load requires bpf_prog_load_opts from v0.6. This creates an
ugly scenario for iproute2 to work across libbpf versions from v0.1
and up.

Since bpf_program_load is only used to load the builtin vrf program,
just remove the libbpf call and use the legacy code.

Signed-off-by: David Ahern <dsahern@kernel.org>