packaging: openwrt fix version string in manifest.

Openwrt splits version from release at the last dash. So, we can't have a dash
as a separator inside the release string (for dirty builds). Use a dot instead.

dist/openwrt/ipk.bzl

@@ -88,7 +88,7 @@ def _ipk_impl(ctx):
             r"scripts/feeds install -a -p scion",
             r"make IB=1 defconfig",  # IB=1 bypasses various unnecessary prerequisites
             r"IFS='-' read tag count commit dirty < ${execroot_abspath}/$5",
-            r'pkgrel=${count}${dirty:+"-dirty$(date +%s)"}',
+            r'pkgrel=${count}${dirty:+".dirty$(date +%s)"}',
             r"make package/feeds/scion/${2}/compile EXECROOT=${execroot_abspath}" +
             ' PKG_VERSION="${tag}" PKG_RELEASE="${pkgrel}"',
             r"cp bin/packages/${6}/scion/${2}_${tag}-${pkgrel}_${6}.ipk ${execroot_abspath}/${4}",