Bump default inline_max up to 1/4 block size

As noted by amgross, the current inline_max default (when littlefs
switches from inline files to CTZ skip-lists) does not match the
theoretical value in DESIGN.md.

The reason for this is 1/8 was chosen as a safer default during
development, due to concerns that 1/4 + mdirs splitting at 1/2 would
lead to poor distribution of large inline files in mdirs.

However, two things have happened since then:

1. Experiments have show "wasted" mdir space is less of a concern than
   initially thought. Extra mdir space contributes to logging, delays
   mdir compaction, and can overall lead to better performance.

2. inline_size was added as a configuration option, so if 1/4 is
   problematic users can always override it.

So bumping this back up to 1/4 may make sense.

lfs.c

@@ -828,9 +828,6 @@ static int lfs_dir_getread(lfs_t *lfs, const lfs_mdir_t *dir,
                 size -= diff;
                 continue;
             }
-
-            // rcache takes priority
-            diff = lfs_min(diff, rcache->off-off);
         }
 
         // load to cache, first condition can no longer fail
@@ -4334,7 +4331,7 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
     LFS_ASSERT(lfs->cfg->inline_max == (lfs_size_t)-1
             || lfs->cfg->inline_max <= ((lfs->cfg->metadata_max)
                 ? lfs->cfg->metadata_max
-                : lfs->cfg->block_size)/8);
+                : lfs->cfg->block_size)/4);
     lfs->inline_max = lfs->cfg->inline_max;
     if (lfs->inline_max == (lfs_size_t)-1) {
         lfs->inline_max = 0;
@@ -4345,7 +4342,7 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
                     lfs->attr_max,
                     ((lfs->cfg->metadata_max)
                         ? lfs->cfg->metadata_max
-                        : lfs->cfg->block_size)/8));
+                        : lfs->cfg->block_size)/4));
     }
 
     // setup default state
@@ -5225,7 +5222,9 @@ static int lfs_fs_gc_(lfs_t *lfs) {
     }
 
     // try to populate the lookahead buffer, unless it's already full
-    if (lfs->lookahead.size < 8*lfs->cfg->lookahead_size) {
+    if (lfs->lookahead.size < lfs_min(
+            8 * lfs->cfg->lookahead_size,
+            lfs->block_count)) {
         err = lfs_alloc_scan(lfs);
         if (err) {
             return err;

lfs.h

@@ -277,7 +277,7 @@ struct lfs_config {
     // Optional upper limit on inlined files in bytes. Inlined files live in
     // metadata and decrease storage requirements, but may be limited to
     // improve metadata-related performance. Must be <= cache_size, <=
-    // attr_max, and <= block_size/8. Defaults to the largest possible
+    // attr_max, and <= block_size/4. Defaults to the largest possible
     // inline_max when zero.
     //
     // Set to -1 to disable inlined files.