add srtp_add_or_update_stream used by telephony/linphone/mediastreamer2

https://gitlab.linphone.org/BC/public/external/srtp/-/commit/c48e27278e656dc4b883044ec85245fb3d22dc51.patch

Index: include/srtp.h
--- include/srtp.h.orig
+++ include/srtp.h
@@ -667,6 +667,31 @@ srtp_err_status_t srtp_update_stream(srtp_t session,
                                      const srtp_policy_t *policy);
 
 /**
+ * @brief srtp_add_or_update_stream() udpates the SRTP stream if it was already initiated or add and initiate it.
+ *
+ * If the session was already initialized,
+ * then the function call srtp_add_or_update_stream(session, policy) updates
+ * the stream(s) in the session that match applying the given
+ * policy and key by calling srtp_update_stream(session, policy). The existing ROC value of all stream(s) will
+ * be preserved.
+ * If the session was not initialized, function srtp_add_stream(session, policy) will be called
+ *
+ * @param session is the SRTP session that contains the streams
+ *        to be updated or added.
+ *
+ * @param policy is the srtp_policy_t struct that describes the policy
+ * for the session.
+ *
+ * @return
+ *    - srtp_err_status_ok           if stream creation succeded.
+ *    - srtp_err_status_alloc_fail   if stream allocation failed
+ *    - srtp_err_status_init_fail    if stream initialization failed.
+ *    - [other]                      otherwise.
+ *
+ */
+srtp_err_status_t srtp_add_or_update_stream(srtp_t session, const srtp_policy_t *policy);
+
+/**
  * @brief srtp_crypto_policy_set_rtp_default() sets a crypto policy
  * structure to the SRTP default policy for RTP protection.
  *