util: move IP route & address object-related functions to virnetdevip.c

util: move IP route & address object-related functions to virnetdevip.c

These functions all need to be called from a utility function that
must be located in the util directory, so we move them all into
util/virnetdevip.[ch] now that it exists.

Function and struct names were appropriately changed for the new
location, but all code is unchanged aside from motion and renaming.