ISA: Clarify "code pointer"

[dthaler]

The "code pointer" inst.imm is actually an instruction offset to code in the BPF program, not an actual memory pointer like "data pointer" is.

A use case is the callback argument to the bpf_loop() helper function.

[dthaler]

Text is ok as is

[dthaler]

Per IETF 119 discussion:

• Change "by address" to "by legacy ID"
• Change "pointer" to "address"

[dthaler]

List discussion at: https://mailarchive.ietf.org/arch/msg/bpf/2JwWQwFdOeMGv0VTbD0CKWwAOEA/

[dthaler]

Proposed change posted at https://mailarchive.ietf.org/arch/msg/bpf/f3Hyx3QnAlgTMaIhr9SRMTL83zA/

[dthaler]

Fixed in draft-02