Added inline_max, to optionally limit the size of inlined files

Inlined files live in metadata and decrease storage requirements, but
may be limited to improve metadata-related performance. This is
especially important given the current plague of metadata performance.

Though decreasing inline_max may make metadata more dense and increase
block usage, so it's important to benchmark if optimizing for speed.

The underlying limits of inlined files haven't changed:
1. Inlined files need to fit in RAM, so <= cache_size
2. Inlined files need to fit in a single attr, so <= attr_max
3. Inlined files need to fit in 1/8 of a block to avoid metadata
   overflow issues, this is after limiting by metadata_max,
   so <= min(metadata_max, block_size)/8

By default, the largest possible inline_max is used. This preserves
backwards compatibility and is probably a good default for most use
cases.

This does have the awkward effect of requiring inline_max=-1 to
indicate disabled inlined files, but I don't think there's a good
way around this.

runners/bench_runner.c

@@ -1322,6 +1322,7 @@ void perm_run(
         .cache_size         = CACHE_SIZE,
         .lookahead_size     = LOOKAHEAD_SIZE,
         .compact_thresh     = COMPACT_THRESH,
+        .inline_max         = INLINE_MAX,
     };
 
     struct lfs_emubd_config bdcfg = {