bpf, docs: Clarify helper ID and pointer terms in instruction-set.rst

bpf, docs: Clarify helper ID and pointer terms in instruction-set.rst

Per IETF 119 meeting discussion and mailing list discussion at
https://mailarchive.ietf.org/arch/msg/bpf/2JwWQwFdOeMGv0VTbD0CKWwAOEA/
the following changes are made.

First, say call by "static ID" rather than call by "address"

Second, change "pointer" to "address"

Signed-off-by: Dave Thaler <dthaler1968@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20240419203617.6850-1-dthaler1968@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>