Import the new logging architecture

This is the new logging architecture, including

* support for multiuple logging targets like stderr and vty
* log levels in addition to categories/subsystems
* filtering based on imsi, i.e. only see events for one subscriber
* dynamically change log level for each category for each vty
diff --git a/openbsc/src/e1_input.c b/openbsc/src/e1_input.c
index 083d8f8..0a0cc8d 100644
--- a/openbsc/src/e1_input.c
+++ b/openbsc/src/e1_input.c
@@ -435,6 +435,8 @@
 				"tei %d, sapi %d\n", tei, sapi);
 			return -EINVAL;
 		}
+
+		debug_set_context(BSC_CTX_BTS, link->trx->bts);
 		switch (link->type) {
 		case E1INP_SIGN_OML:
 			msg->trx = link->trx;