Working towards a goal...

[Warner Losh]

So, I'm working towards a goal of having the routines that live in
sys/cam/*.c never ever reference scsi, ata or nvme (or sdio or ...).
there's way too many places where you have to add code when you add a
transport and as evidenced by my recent (a) mismerged from the netflix
tree and (b) the subsequent subtle breakage when I did, I think this
needs to change.

Before I go too nuts down this path, I thought I'd poll here for
sentiment. Here's a review that starts to implement things by turning
the XPORTs into a linker set.

https://reviews.freebsd.org/D7289

Warner