Rename plural to singular; cleaner and more consistent with 'ip' utility

examples/route_lo.rb

@@ -7,10 +7,10 @@ require 'netlink/route'
 # Example of use of low-level API for NETLINK_ROUTE socket.
 # Each of these method calls performs a netlink protocol exchange.
 
-rt = Netlink::Route::Socket.new
+ip = Netlink::Route::Socket.new
 puts "*** links ***"
-pp rt.links.read_links
+pp ip.link.read_link
 puts "*** addrs ***"
-pp rt.addrs.read_addrs
+pp ip.addr.read_addr
 puts "*** routes ***"
-pp rt.routes.read_routes
+pp ip.route.read_route