libbpf: add support for bpf_call

- recognize relocation emitted by llvm
- since all regular function will be kept in .text section and llvm
  takes care of pc-relative offsets in bpf_call instruction
  simply copy all of .text to relevant program section while adjusting
  bpf_call instructions in program section to point to newly copied
  body of instructions from .text
- do so for all programs in the elf file
- set all programs types to the one passed to bpf_prog_load()

Note for elf files with multiple programs that use different
functions in .text section we need to do 'linker' style logic.
This work is still TBD

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/lib/bpf/bpf.h

@@ -40,7 +40,7 @@ int bpf_create_map_in_map(enum bpf_map_type map_type, const char *name,
 			  __u32 map_flags);
 
 /* Recommend log buffer size */
-#define BPF_LOG_BUF_SIZE 65536
+#define BPF_LOG_BUF_SIZE (256 * 1024)
 int bpf_load_program_name(enum bpf_prog_type type, const char *name,
 			  const struct bpf_insn *insns,
 			  size_t insns_cnt, const char *license,