asan: heap-buffer-overflow in bpf_elf_generic_reloc

asan: heap-buffer-overflow in bpf_elf_generic_reloc

The bpf reloc howtos are a bit weird, using bitpos to specify an
offset from r_offset that is outside the size of the reloc as given by
howto.size.  That means bfd_get_reloc_size gives the wrong answer for
range checking, and thus bfd_reloc_offset_in_range can't be used.

	* elf64-bpf.c (bpf_elf_generic_reloc): Handle bitpos offset reloc
	range checking.