overlay: fix data race in map access
overlay: fix data race in map access

Signed-off-by: Alexander Morozov <2043cda4df124b840b98ee1c4307c199042efdf7@gmail.com>

WeiZhang555/libnetwork,curtiszimmerman/libnetwork,YujiOshima/libnetwork,vdemeester/libnetwork,sainath14/libnetwork,docker/libnetwork,medallia/libnetwork,mYmNeo/libnetwork,YujiOshima/libnetwork,msabansal/libnetwork,allencloud/libnetwork,ityangchen/libnetwork,vdemeester/libnetwork,WeiZhang555/libnetwork,mbanikazemi/libnetwork,vdemeester/libnetwork,fcrisciani/libnetwork,abhi/libnetwork,tmakita/libnetwork,mahak/libnetwork,cpuguy83/libnetwork,allencloud/libnetwork,docker/libnetwork,kolyshkin/libnetwork,medallia/libnetwork,mbanikazemi/libnetwork,fcrisciani/libnetwork,cpuguy83/libnetwork,abhi/libnetwork,mahak/libnetwork,tmakita/libnetwork,mYmNeo/libnetwork,docker/libnetwork,ityangchen/libnetwork,kolyshkin/libnetwork,sainath14/libnetwork,mahak/libnetwork,kolyshkin/libnetwork,msabansal/libnetwork,medallia/libnetwork,abhi/libnetwork,curtiszimmerman/libnetwork