Jormungandr: take crow fly mode a a fall back mode in tags
Jormungandr: do not call walking and bss

if bss and walking are enable as fallback mode, we need only to call for
the bss fallback mode since it will enable walking (if it's better than
bss)

that way we can save some kraken calls
Merge pull request #524 from antoine-de/better_mode_tag

Jormungandr: take crow fly mode a a fall back mode in tags