Clarify, document Assignment related timers

Related: OS#3928
Change-Id: Iad31a5c6f83cd78793adf05a6af782ceacae8b11
diff --git a/src/gprs_pcu.c b/src/gprs_pcu.c
index 226b861..3875e09 100644
--- a/src/gprs_pcu.c
+++ b/src/gprs_pcu.c
@@ -37,8 +37,8 @@
 	{ .T=PCU_TDEF_SI_CACHE_ALIVE,      .default_val=5,  .unit=OSMO_TDEF_S,   .desc="[RAC+CI]->[SI] resolution cache entry storage timeout (s)", .val=0 },
 	{ .T=-101,  .default_val=30,  .unit=OSMO_TDEF_S,  .desc="BSSGP (un)blocking procedures timer (s)",  .val=0 },
 	{ .T=-102,  .default_val=30,  .unit=OSMO_TDEF_S,  .desc="BSSGP reset procedure timer (s)",          .val=0 },
-	{ .T=-2000, .default_val=2,   .unit=OSMO_TDEF_MS, .desc="Tbf reject for PRR timer (ms)",            .val=0 },
-	{ .T=-2001, .default_val=2,   .unit=OSMO_TDEF_S,  .desc="PACCH assignment timer (s)",               .val=0 },
+	{ .T=-2000, .default_val=2,   .unit=OSMO_TDEF_MS, .desc="Delay release of UL TBF after tx Packet Access Reject (PACCH) (ms)", .val=0 },
+	{ .T=-2001, .default_val=2,   .unit=OSMO_TDEF_S,  .desc="PACCH assignment timeout (s)",               .val=0 },
 	{ .T=-2002, .default_val=200, .unit=OSMO_TDEF_MS, .desc="Waiting after IMM.ASS confirm timer (ms)", .val=0 },
 	{ .T=-2030, .default_val=60,  .unit=OSMO_TDEF_S,  .desc="Time to keep an idle MS object alive (s)", .val=0 }, /* slightly above T3314 (default 44s, 24.008, 11.2.2) */
 	{ .T=-2031, .default_val=2000, .unit=OSMO_TDEF_MS, .desc="Time to keep an idle DL TBF alive (ms)",  .val=0 },