Fix crash on bonding + NFS root.

In the case that a system is booted diskless with NFS root, such as in a cluster I am building, then the OpenRC default behavior crashes the system.  A new 'subsume_bond&lt;x&gt;="&lt;kernel-autoconfigured-iface&gt;"' option in /etc/conf.d/net is implemented to resolve the issue, and a warning is added where bonding is used on systems with root on NFS in order to advertise the solution.