Update init-ifupdown_%.bbappend

Resolve this issue "ERROR: ExpansionError during parsing /home/imx6/wb-daisy/sources/poky/meta/recipes-core/init-ifupdown/init-ifupdown_1.0.bb: Failure expanding variable do_fetch[file-checksums], expression was ${@bb.fetch.get_checksum_file_list(d)} which triggered exception MalformedUrl: The URL: 'interfaces-wlan0-ap' is invalid and cannot be interpreted"
http://forums.wandboard.org/viewtopic.php?f=12&t=126&st=0&sk=t&sd=a&sid=badd14dc4bef436e67a99ee4b15e8103&start=40