subscriber: set `log` max level when reloading (#1270)
This modifies the `tracing_subscriber::reload` layer to also set the
`log` crate's max level with the current max `tracing` level filter
after reloading. If reloading the subscriber caused the max `tracing`
level to change, this ensures that the change is propagated to the `log`
crate as well. In the case where the max level was made more verbose,
this will ensure that `log` records which were previously disabled are
enabled correctly; in the case where it was made less verbose, this
improve performance by not having to perfrom more costly filtering for
those `log` records.
The `log` max level is set only after rebuilding the callsite interest
cache, which is what sets the max `tracing` level filter. This ensures
that we pass the latest state to the `log` crate.
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
