lapd/lapdm: print user-defined string name instead of (dl=%p)

At the moment we print the pointer address to identify the log lines
belonging to a specific connection. Since pointer addresses are
difficult to work with, a human readable ID should be printed instead.

e.g. "This is LAPD instance for SAPI3 on bts0/trx1/ts5/lchan3"

Change-Id: Ie6742843fff809edffcac24c4dce4edf66bc71be
Closes: OS#1938
diff --git a/TODO-RELEASE b/TODO-RELEASE
index c9d9c56..2d65372 100644
--- a/TODO-RELEASE
+++ b/TODO-RELEASE
@@ -12,3 +12,4 @@
 sim		API/ABI change		all over the place
 gsm		new API			new osmo_bts_unset_feature()
 gb		API/ABI change		deprecate gprs_nsvc_crate(); export gprs_nsvc_create2()
+gsm		API/ABI change		add new member to lapd_datalink