resources.conf.prod: Use different ARFCN for sysmocell-5k

Due to a bug in sysmocell-5K's TRX implementation, it may keep polluting
the air transmitting after the BTS is disconnected. This could cause
interferences with other tests. Correct fix would be to RF lock it after
test finishes (through ccli), but let's simply use a different ARFCN for
now.

Related: OS#4129
Change-Id: I6d5555aa8740b262ee92110987189c076db44f76

example/resources.conf.prod

@@ -69,6 +69,8 @@ bts:
   addr: 10.42.42.51
   band: GSM-1800
   ciphers: [a5_0, a5_1]
+  trx_list:
+    - arfcn: 878
   osmo_trx:
         launch_trx: false
         clock_reference: external

src/osmo_gsm_tester/resource.py

@@ -60,6 +60,7 @@ RESOURCES_SCHEMA = {
         'bts[].num_trx': schema.UINT,
         'bts[].max_trx': schema.UINT,
         'bts[].trx_list[].addr': schema.IPV4,
+        'bts[].trx_list[].arfcn': schema.INT,
         'bts[].trx_list[].hw_addr': schema.HWADDR,
         'bts[].trx_list[].net_device': schema.STR,
         'bts[].trx_list[].nominal_power': schema.UINT,