Deprecate using NET_C without HAVE_IPV6

ChangeLog

diff --git a/ChangeLog b/ChangeLog
index 8c28c51..f56b204 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -43,6 +43,7 @@
      curve picked by the server was actually allowed.
 
 Changes
+   * Enabling POLARSSL_NET_C without POLARSSL_HAVE_IPV6 is deprecated.
    * compat-1.2.h and openssl.h are deprecated.
    * Adjusting/overriding CFLAGS and LDFLAGS with the make build syste is now
      more flexible (warning: OFLAGS is not used any more) (see the README)