Make gcc 11.1.0 false positivies happy

After my system's gcc was upgraded, I get false positivies like the one
below:
"""
/git/osmo-pcu/src/gprs_bssgp_pcu.c: In function ‘ns_configure_nse’:
/git/osmo-pcu/src/gprs_bssgp_pcu.c:1103:58: error: ‘%d’ directive output may be truncated writing between 1 and 11 bytes into a region of size 2 [-Werror=format-truncation=]
 1103 |                         snprintf(name, sizeof(name), "pcu%d", i);
      |                                                          ^~
/git/osmo-pcu/src/gprs_bssgp_pcu.c:1103:54: note: directive argument in the range [-2147483648, 1]
 1103 |                         snprintf(name, sizeof(name), "pcu%d", i);
      |                                                      ^~~~~~~
/git/osmo-pcu/src/gprs_bssgp_pcu.c:1103:25: note: ‘snprintf’ output between 5 and 15 bytes into a destination of size 5
 1103 |                         snprintf(name, sizeof(name), "pcu%d", i);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"""
In this case, i can't never take a value with more than 1 digit, but gcc
seems to be unable to see that.

Let's increase the buffer size a few bytes to make gcc happy, and make
the variable unsigned since it never will get negative values.

Next change is also a false positive, since variables are always
initialized beforehand in the cod epaths where they are used:
"""
/git/osmo-pcu/src/bts.cpp: In function ‘int bts_rcv_rach(gprs_rlcmac_bts*, const rach_ind_params*)’:
/git/osmo-pcu/src/bts.cpp:859:25: error: ‘ts_no’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  859 |         uint8_t trx_no, ts_no;
      |                         ^~~~~
/git/osmo-pcu/src/bts.cpp:859:17: error: ‘trx_no’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
  859 |         uint8_t trx_no, ts_no;
      |                 ^~~~~~
"""

Change-Id: I1362a335a0c761bde367dbc779de4afa88f13584
diff --git a/src/bts.cpp b/src/bts.cpp
index 95dde04..ee6b915 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -856,7 +856,7 @@
 	struct chan_req_params chan_req = { 0 };
 	struct gprs_rlcmac_ul_tbf *tbf = NULL;
 	struct gprs_rlcmac_sba *sba;
-	uint8_t trx_no, ts_no;
+	uint8_t trx_no = 0, ts_no = 0; /* initialize to avoid uninitialized false warnings on some gcc versions (11.1.0) */
 	uint32_t sb_fn = 0;
 	uint8_t usf = 7;
 	uint8_t tsc = 0;