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This commit does two interleaved things:

* finis Multi-Arch support by changing dirs names, missing in commit:
   637406a0

 ("iptables: make it Multi-Arch: foreign")

* move libs from /lib to /usr/lib/

Therefore, the final change is, for example:
 /lib -> /usr/lib/x86_64-linux-gnu

Files already under /usr/lib are simply moved to /usr/lib/<arch>
Signed-off-by: Arturo Borrero Gonzalez <arturo.borrero.glez@gmail.com>