vfs: add VNPASS macro and augment VNASSERT to print more about the assert

[mjg]

Summary

Inspired by MPASS.

VNPASS repeats the first line for panicstr, I don't know if that's a problem apart from looking weird.

Sample output:

VNASSERT failed: vp->v_holdcnt == 1234 not true at /usr/src/sys/kern/vfs_subr.c:3148 (vputx)
0xfffff80003ba71e8: type VDIR
    usecount 7, writecount 0, refcount 1 mountedhere 0
    flags (VV_ROOT)
    lock type devfs: EXCL by thread 0xfffff800027d96e0 (pid 1, kernel, tid 100002)
panic: foo test

VNASSERT failed: vp->v_holdcnt == 1234 not true at /usr/src/sys/kern/vfs_subr.c:3148 (vputx)
0xfffff80003ba51e8: type VDIR
    usecount 7, writecount 0, refcount 1 mountedhere 0
    flags (VV_ROOT)
    lock type devfs: EXCL by thread 0xfffff800027d96e0 (pid 1, kernel, tid 100002)
panic: condition vp->v_holdcnt == 1234 not met at /usr/src/sys/kern/vfs_subr.c:3148 (vputx)

[kib]

I would also change VNASSERT in the way you proposed.

[mjg]

• augment VNASSERT