confusion about root partition causes panic during startup

I installed an additional NVME drive on a system, and then booted.  It turns
out that the new drive became nda0, renumbering the other drives.  The loader
found the correct partition to boot (the only choice), and loaded the kernel
correctly.  However, /etc/fstab still had the old name (nvd1p2), which is
now drive 2.  I expected it to drop into single user, but instead the system
panicked in vfs_mountroot_shuffle trying to switch root devices (see below).
It doesn't seem that having the wrong root device in /etc/fstab should cause
a panic; it makes it harder to patch the system.  I was unable to get the
system to boot using boot-to-single-user or setting currdev, but I managed
to remember doing "boot -a" from a loader prompt to get the system to ask
the root device before mounting it.  I can easily reproduce this to test.
Probably the NDFREE_PNBUF() shouldn't happen if namei() returned an error.

		Mike

Trying to mount root from ufs:/dev/nvd1p2 [rw]...
WARNING: WITNESS option enabled, expect reduced performance.
mountroot: unable to remount devfs under /dev (error 2)
panic: Assertion _ndp->ni_cnd.cn_pnbuf != NULL failed at ../../../kern/vfs_mountroot.c:416
cpuid = 19
time = 11
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe006d3bac40
vpanic() at vpanic+0x149/frame 0xfffffe006d3bac90
panic() at panic+0x43/frame 0xfffffe006d3bacf0
vfs_mountroot() at vfs_mountroot+0x1bf7/frame 0xfffffe006d3bae60
start_init() at start_init+0x23/frame 0xfffffe006d3baef0
fork_exit() at fork_exit+0x82/frame 0xfffffe006d3baf30
fork_trampoline() at fork_trampoline+0xe/frame 0xfffffe006d3baf30
--- trap 0x5c035c02, rip = 0x680c680c680c680c, rsp = 0x1b6b1f6b1b6b1b6b, rbp = 0x4eb54eb54eb54eb5 ---
KDB: enter: panic
[ thread pid 1 tid 100002 ]
Stopped at      kdb_enter+0x32: movq    $0,0xde7643(%rip)