def resize(prefix_len)
			m32 = Mask32.new(prefix_len)
			return IPv4Net.new(self.network,m32)
		end
def resize(prefix_len)
			m32 = Mask32.new(prefix_len)
			return IPv4Net.new(self.network,m32)
		end
resize returns a copy of the network with an adjusted netmask.
 Throws ValidationError on invalid prefix_len.