multilib.conf: Workaround opkg multilib issues

multilib.conf: Workaround opkg multilib issues

Multilib with opkg hasn't worked since the --force-overwrite option was dropped in
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=88a9f6db3482623c9cb54fb03db1045051cec9f6

Since we merged the libexecdir changes, we also need the --force-maintainer flag
to avoid conf file conflicts.

Both these changes are suboptimal however the alternative is completely broken and
these changes only affect people who have multilibs enabled and use opkg.

[YOCTO #3453]

(From OE-Core rev: 6310e66cd62aab6109027a8dce9c56bf721bea92)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>