After a kernel, nfs-client and nfs-kernel-server (and more packages) update the changes in /usr/lib/systemd/scripts/nfs-utils_env.sh were reverted. I have re-applied them but now after I restarted the system with rpcbind.socket masked, rpcbind is still started. However there are no boot pauses now, the boot time is normal. It seems that only when rpcbind is not started the system gets stuck at boot time or booting is slow as hell.