mount: let a readdirplus stop taking references at a cap

The inode table only shrinks when the kernel returns a reference, so a walk
over a large tree grows it with every child it touches and nothing gives any
of it back until the kernel reclaims dentries. On a mount with tens of
millions of files that is most of the process's heap.

-maxInodeEntries stops the speculative half of that. Past the cap a
readdirplus still reports every name, but leaves the EntryOut zeroed: Linux
reads a zero nodeid as 'no attributes for this entry', takes no reference, and
looks up the ones the client actually needs. A LOOKUP is never refused, so the
table can still grow past the cap by what a client really asks for, and
nothing here evicts. Default 0 keeps today's behavior.

weed/command/mount_common.go

@@ -204,6 +204,7 @@ func buildSeaweedFileSystem(option *MountOptions, p fileSystemParams) *mount.WFS
 		WriteBufferSizeMB:           *option.writeBufferSizeMB,
 		CacheMetaTTlSec:             *option.cacheMetaTtlSec,
 		CacheDirMaxEntries:          *option.cacheDirMaxEntries,
+		MaxInodeEntries:             *option.maxInodeEntries,
 		DataCenter:                  *option.dataCenter,
 		Quota:                       int64(*option.collectionQuota) * 1024 * 1024,
 		LogicalDiskUsage:            *option.logicalDiskUsage,