[oe] Fix for ipkg->opkg transition breakage

[Rod Whitby]

I have added the following line to rootfs_ipk.bbclass to allow distros 
that have not transitioned to using opkg in the target rootfs (as 
opposed to opkg being used by the build system to create the rootfs) to 
continue working as they did before with only an additional symlink's 
worth of space used in the rootfs and no change to the user experience.

============================================================
--- classes/rootfs_ipk.bbclass  c319cef6215ceb9e757092d0eb6ea8303cbaacad
+++ classes/rootfs_ipk.bbclass  f2e739e3ef76b513c9eded6b230ecdd3e8f71886
@@ -60,6 +60,9 @@ fakeroot rootfs_ipk_do_rootfs () {

         rm -f ${IMAGE_ROOTFS}${libdir}/opkg/lists/*

+       # Keep this line until package manager selection is implemented
+       ln -s opkg ${IMAGE_ROOTFS}${sysconfdir}/ipkg
+
         ${ROOTFS_POSTPROCESS_COMMAND}

         log_check rootfs

-- Rod