Support sending OML Alerts via BTS

* extend BTS <-> PCU protocol with TXT messages
* use it to implement OML alerts support
* use it to implement version message
* add function to transmit both of them them
* send alerts for internal encoding problems as an example
* send version when BTS socket is connected

Note: requires corresponding change
If57459c0610f2c7b36d599b13087c8deef8bdd9e in libosmocore.

Related: OS#1614, 1615
Change-Id: If4ea5b3f7409df2fb030681ad468df6b711790a7
diff --git a/src/osmobts_sock.cpp b/src/osmobts_sock.cpp
index d542b66..d7e55e7 100644
--- a/src/osmobts_sock.cpp
+++ b/src/osmobts_sock.cpp
@@ -287,6 +287,9 @@
 
 	pcu_sock_state = state;
 
+	LOGP(DL1IF, LOGL_INFO, "Sending version %s to BTS.\n", PACKAGE_VERSION);
+	pcu_tx_txt_ind(PCU_VERSION, "%s", PACKAGE_VERSION);
+
 	return 0;
 }