bpf: offload: make bpf_offload_dev_match() reject host+host case

Daniel suggests it would be more logical for bpf_offload_dev_match()
to return false is either the program or the map are not offloaded,
rather than treating the both not offloaded case as a "matching
CPU/host device".

This makes no functional difference today, since verifier only calls
bpf_offload_dev_match() when one of the objects is offloaded.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>