add srtp_add_or_update_stream used by telephony/linphone/mediastreamer2

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

Index: srtp/srtp.c
--- srtp/srtp.c.orig
+++ srtp/srtp.c
@@ -2903,6 +2903,19 @@ srtp_err_status_t srtp_dealloc(srtp_t session)
     return srtp_err_status_ok;
 }
 
+srtp_err_status_t srtp_add_or_update_stream(srtp_t session, const srtp_policy_t *policy)
+{
+    srtp_err_status_t status;
+    // Update streams if the session was already initialized
+    if (session->stream_template) {
+        status = srtp_update_stream(session, policy);
+    } else {
+        status = srtp_add_stream(session, policy);
+    }
+
+    return status;
+}
+
 srtp_err_status_t srtp_add_stream(srtp_t session, const srtp_policy_t *policy)
 {
     srtp_err_status_t status;