Clarify write_immediate_assignment() signature

* remove unused variable
* use bool for boolean types
* add clarification comments

Change-Id: I363445063e2d873d9194b2a5924b9e59b8b7ea53
diff --git a/src/tbf.cpp b/src/tbf.cpp
index 233ae91..ffe8b82 100644
--- a/src/tbf.cpp
+++ b/src/tbf.cpp
@@ -880,7 +880,7 @@
 			LOGPTBF(dl_tbf, LOGL_DEBUG, "Re-send dowlink assignment on PCH (IMSI=%s)\n",
 				imsi());
 			/* send immediate assignment */
-			dl_tbf->bts->snd_dl_ass(dl_tbf, 0, imsi());
+			dl_tbf->bts->snd_dl_ass(dl_tbf, false, imsi());
 			dl_tbf->m_wait_confirm = 1;
 		}
 	} else