wspr/nacl: Changes to run WSPR in nacl

Change-Id: Ica3a46b28ef1cf0574b5ae6cf5948467374665f7
diff --git a/lib/netconfig/ipaux_linux.go b/lib/netconfig/ipaux_linux.go
index 49945d1..4003001 100644
--- a/lib/netconfig/ipaux_linux.go
+++ b/lib/netconfig/ipaux_linux.go
@@ -1,3 +1,5 @@
+// +build linux
+
 package netconfig
 
 // We connect to the Netlink Route socket and parse messages to