Support new ip=... kernel format, supporting nameserver IPs

[mika]

As of torvalds/linux@5e95377 the ip=... kernel option supports nameserver IPs.

Our live-boot-grml uses a different ip=... format than upstream live-boot project (which has its own standard), our implementation is based on the one from the kernel, though the nameserver IPs aren't supported yet (we dns=... instead).

Would be nice to support the option identical to what the linux kernel uses/provides.

Thanks to András Korn for raising this on IRC.