Fix an issue where a 200 Ok for REGISTER coming from an upstream server is not routed back the originator of the REGISTER, but instead discarded. This happens in relay-reg-to-domains mode, when RegistrarDb uses the redis backend, because the ResponseSipEvent associated with the 200Ok is suspended and later resumed. Meanwhile, the outgoing transaction associated with this 200 Ok is terminated, causing properties to be cleared. Subsequently, when the 200 Ok crosses the module::Router, it cannot be associated with the ForkContext, because the outgoing transaction no longer references the ForkContext in its properties. The solution implemented consists automatically protect the transaction's properties when the SipEvent enters the SUSPENDED state, and unprotect them when the SipEvent reaches the TERMINATED state.