fscache: Select netfs stats if fscache stats are enabled

Unconditionally select the stats produced by the netfs lib if fscache stats
are enabled as the former are displayed in the latter's procfile.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-cachefs@redhat.com
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Link: https://lore.kernel.org/r/162280352566.3319242.10615341893991206961.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/162431189627.2908479.9165349423842063755.stgit@warthog.procyon.org.uk/