nvme: Always lock and only avoid processing for recovery state

When we lose a race with the timeout code, shift towards waiting for
that timeout code to complete so we can acquire the lock. This way we
can make sure we're in 'normal' mode before processing I/O
completions. If we're not in 'normal' mode, then we're resetting and we
should avoid completions.

Sponsored by: Netflix
Reviewed by: gallatin
Differential Revision: https://reviews.freebsd.org/D46024