opkg: update to latest Git HEAD

opkg: update to latest Git HEAD

f2166a8 libopkg: implement lightweight package listing logic
cf4554d libopkg: support passing callbacks to feed parsing functions
2a0210f opkg-cl: don't read feeds on opkg update
b6f1967 libopkg: use xsystem() to spawn opkg-key
60b9af2 file_util.c: refactor and fix checksum_hex2bin()
206ebae file_util.c: fix possible bad memory access in file_read_line_alloc()

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit 79da9d78b98e1cd4574a37e2c4c5f8315b91563d)