nvmecontrol: Create letoh generically convert to host order

[imp]

Summary

Using _Generic, create LE2H which will generically convert uintXX_t
types from little endian to host, regardless of the size.

USE jhb's suggested name

Sponsored by: Netflix

[chuck]

amazeballs!

[jhb]

I kind of wonder if we'd like to just have this in <sys/endian.h> as letoh, but then you'd want the full complement of betoh, htobe, etc.

sbin/nvmecontrol/nvmecontrol.h

64

[imp]

In D44649#1019208, @jhb wrote:

I kind of wonder if we'd like to just have this in <sys/endian.h> as letoh, but then you'd want the full complement of betoh, htobe, etc.

I'll convert to letoh, but leave the others for now because the be ones aren't needed and htole is harder as a macro and I'm not quite ready for it.