Set fallbackPort to 0 in SetTLSPortPolicy

The default fallback port should be reset to 0 when setting the TLS port policy. This ensures the fallbackPort does not retain an incorrect value when switching policies.

client.go

@@ -751,6 +751,7 @@ func (c *Client) SetTLSPolicy(policy TLSPolicy) {
 func (c *Client) SetTLSPortPolicy(policy TLSPolicy) {
 	if c.port == DefaultPort {
 		c.port = DefaultPortTLS
+		c.fallbackPort = 0
 
 		if policy == TLSOpportunistic {
 			c.fallbackPort = DefaultPort