TBF-DL: mark rcvd_dl_ack() parameters as boolean

The final(_ack) parameter of rcvd_dl_ack() only used as boolean - mark
it as such.

Change-Id: Icc4d68f049a45d4b42c5594f50594ff0d44c1bac
diff --git a/src/tbf_dl.cpp b/src/tbf_dl.cpp
index 84f6166..58b55dc 100644
--- a/src/tbf_dl.cpp
+++ b/src/tbf_dl.cpp
@@ -1159,7 +1159,7 @@
 	return 0;
 }
 
-int gprs_rlcmac_dl_tbf::rcvd_dl_ack(uint8_t final_ack, unsigned first_bsn,
+int gprs_rlcmac_dl_tbf::rcvd_dl_ack(bool final_ack, unsigned first_bsn,
 	struct bitvec *rbb)
 {
 	int rc;
@@ -1179,7 +1179,7 @@
 	return rc;
 }
 
-int gprs_rlcmac_dl_tbf::rcvd_dl_ack(uint8_t final_ack, uint8_t ssn, uint8_t *rbb)
+int gprs_rlcmac_dl_tbf::rcvd_dl_ack(bool final_ack, uint8_t ssn, uint8_t *rbb)
 {
 	LOGPTBFDL(this, LOGL_DEBUG, "downlink acknowledge\n");