find `ip` via $PATH and not hardcoded path

https://bugs.gentoo.org/480636

--- a/client/scripts/linux
+++ b/client/scripts/linux
@@ -23,7 +23,7 @@
 # of the $1 in its args.
 
 # 'ip' just looks too weird.  /sbin/ip looks less weird.
-ip=/sbin/ip
+ip=ip
 
 make_resolv_conf() {
   if [ x"$PEER_DNS" != x ] && [ x"$PEER_DNS" != xyes ]; then