bpf: jmp_offset() and verbose_insn() utility functions

Extract two utility functions:
- One BPF jump instruction uses .imm field to encode jump offset,
  while the rest use .off. Encapsulate this detail as jmp_offset()
  function.
- Avoid duplicating instruction printing callback definitions by
  defining a verbose_insn() function, which disassembles an
  instruction into the verifier log while hiding this detail.

These functions will be used in the next patch.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250304195024.2478889-2-eddyz87@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>