Make 'port' a string in NET module

- avoids dependency on snprintf
- allows using "smtps" instead of "456" if desired
diff --git a/ChangeLog b/ChangeLog
index 0edbd16..6ba45ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -92,6 +92,7 @@
      in config.h
    * net_connect() and net_bind() have a new 'proto' argument to choose
      between TCP and UDP, using the macros NET_PROTO_TCP or NET_PROTO_UDP.
+     Their 'port' argument type is changed to a string.
    * Some constness fixes
 
 Removals