sndcp: Fixups for sndcp layer based on coverity-scan suggestions

- missing break in gprs_sndcp_pcomp.c, line 143
- string overflow in slhc_test.c, line 211
- sizeof mismatch in gprs_sndcp_xid.c, line 1369 and 1378
- mismatching signedness in gprs_sndcp_xid.c, line 1377
- needless < 0 comparison in gprs_sndcp_xid.c, line 477
- needless < 0 comparison in gprs_sndcp_xid.c, line 209
- missing returncode check in v42bis_test.c, line 320
- wrong pointer dereferentialization in gprs_sndcp_comp.c, line 73

Change-Id: I4f9adf251f5119e67ffe76baad6f1f996ac8dbad
diff --git a/openbsc/src/gprs/gprs_sndcp_comp.c b/openbsc/src/gprs/gprs_sndcp_comp.c
index b13cb8b..cae0039 100644
--- a/openbsc/src/gprs/gprs_sndcp_comp.c
+++ b/openbsc/src/gprs/gprs_sndcp_comp.c
@@ -70,7 +70,7 @@
 		       comp_field->v42bis_params->nsapi,
 		       sizeof(comp_entity->nsapi));
 	} else if (comp_field->v44_params) {
-		comp_entity->nsapi_len = comp_field->v42bis_params->nsapi_len;
+		comp_entity->nsapi_len = comp_field->v44_params->nsapi_len;
 		memcpy(comp_entity->nsapi,
 		       comp_field->v42bis_params->nsapi,
 		       sizeof(comp_entity->nsapi));