networkdb: fix race in access to nodes len
networkdb: fix race in access to nodes len

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

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