Use unique incrementing value for BTS LAC

Change-Id: I9f864bac05e39ec2fc305f774194799c3d8fe1b0
diff --git a/src/osmo_gsm_tester/suite.py b/src/osmo_gsm_tester/suite.py
index 28bdd69..9f9421e 100644
--- a/src/osmo_gsm_tester/suite.py
+++ b/src/osmo_gsm_tester/suite.py
@@ -344,6 +344,7 @@
 
     def bts(self, specifics=None):
         bts = bts_obj(self, self.reserved_resources.get(resource.R_BTS, specifics=specifics))
+        bts.set_lac(self.lac())
         self.register_for_cleanup(bts)
         return bts
 
@@ -370,6 +371,11 @@
         self.log('using MSISDN', msisdn)
         return msisdn
 
+    def lac(self):
+        lac = self.resources_pool.next_lac(self)
+        self.log('using LAC', lac)
+        return lac
+
     def poll(self):
         if self._processes:
             for process in self._processes: