virtio: use bool for boolean functions

[freebsd_igalic.co]

Summary

these static functions:

• vq_ring_use_indirect

and these public functions:

• virtio_bus_is_modern
• virtio_with_feature
• virtqueue_empty
• virtqueue_full

exclusively return a boolean value.
Change their return values to bool.

Sponsored by: The FreeBSD Foundation

[cognet]

sys/dev/virtio/pci/virtio_pci_legacy.c

91

Hmm those int arguments, disappearing from the virtqueues method, should probably not be removed in that commit :)

sys/dev/virtio/pci/virtio_pci_modern.c

116

ditto

[freebsd_igalic.co]

sys/dev/virtio/pci/virtio_pci_legacy.c

91

thanks for catching that.
looks like a botched rebase

[freebsd_igalic.co]

thanks to @cognet for helping catch this rebase fuckup.

[freebsd_igalic.co]

I reckon this commit can easily be MFC'd without causing too much breakage