libbpf: Add doxygen documentation for bpf_prog_* APIs in bpf.h

Add doxygen comment blocks for all public bpf_prog_* APIs in
tools/lib/bpf/bpf.h. These doc comments are for:

-bpf_prog_load()
-bpf_prog_attach()
-bpf_prog_detach()
-bpf_prog_detach2()
-bpf_prog_get_next_id()
-bpf_prog_get_fd_by_id()
-bpf_prog_get_fd_by_id_opts()
-bpf_prog_query()
-bpf_prog_bind_map()
-bpf_prog_test_run_opts()

Signed-off-by: Jianyun Gao <[email protected]>

Author: Jianyun Gao