build: Drop down to 50 layers for chunked images

It seems that (at least older?) containers/storage barfs on this, so let's drop
down a good bit.

(We could also change the ostree upstream default, but...mmm, perhaps
 later)

src/cmd-build

@@ -386,7 +386,7 @@ else
     case "${ostree_format}" in
         oci) ;;
         # Note rpm-ostree always copies the rpmostree.inputhash key
-        oci-chunked) cmd=(rpm-ostree container-encapsulate) ;;
+        oci-chunked) cmd=(rpm-ostree container-encapsulate --max-layers=$MAX_OSTREECONTAINER_LAYERS) ;;
         *) fatal "Unknown ostree-format: ${ostree_format}"
     esac
     runv "${cmd[@]}" --repo="${tmprepo}" \

src/cmdlib.sh

@@ -36,6 +36,12 @@ export basearch
 arch=$(uname -m)
 export arch
 
+# The ostree-ext default is 64, but this is still too much apparently
+# for (older?) versions of podman AKA containers/storage (or maybe)
+# a kernel limitation?  For example
+# `cannot mount layer, mount label "" too large 4168 > page size 4096`
+MAX_OSTREECONTAINER_LAYERS=50
+
 case $arch in
     "x86_64")  DEFAULT_TERMINAL="ttyS0"   ;;
     "ppc64le") DEFAULT_TERMINAL="hvc0"    ;;