Use negated option for controlling TLS support.

A positive option looks better, but comes with the following compatibility
issue: people using a custom config.h that is not based on the default
config.h and need TLS support would need to manually change their config in
order to still get TLS.

Work around that by making the public option negative. Internally the positive
option is used, though.

In the future (when preparing the next major version), we might want to switch
back to a positive option as this would be more consistent with other options
we have.
diff --git a/scripts/config.pl b/scripts/config.pl
index 86af553..ed9aa02 100755
--- a/scripts/config.pl
+++ b/scripts/config.pl
@@ -31,6 +31,7 @@
 #   MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 #   MBEDTLS_REMOVE_3DES_CIPHERSUITES
 #   MBEDTLS_SSL_HW_RECORD_ACCEL
+#   MBEDTLS_SSL_PROTO_NO_DTLS
 #   MBEDTLS_RSA_NO_CRT
 #   MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
 #   MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
@@ -92,6 +93,7 @@
 MBEDTLS_REMOVE_ARC4_CIPHERSUITES
 MBEDTLS_REMOVE_3DES_CIPHERSUITES
 MBEDTLS_SSL_HW_RECORD_ACCEL
+MBEDTLS_SSL_PROTO_NO_TLS
 MBEDTLS_X509_ALLOW_EXTENSIONS_NON_V3
 MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION
 MBEDTLS_ZLIB_SUPPORT