bssgp: Make BVC bucket size / leak rate configurable

Currently the FLOW-CONTROL_BVC message contains fixed values: The tag
is 1, the BVC bucket size is 6MB, the BVC bucket leak rate is
820kbit/s, the MS bucket size is 50kB, and the MS leak rate is
50kbit/s.

This commit makes the BVC parameters configurable and adds the
following VTY commands:

- flow-control force-bvc-bucket-size <1-6553500>
- no flow-control force-bvc-bucket-size
- flow-control force-bvc-leak-rate <1-6553500>
- no flow-control force-bvc-leak-rate
- flow-control force-ms-bucket-size <1-6553500>
- no flow-control force-ms-bucket-size
- flow-control force-ms-leak-rate <1-6553500>
- no flow-control force-ms-leak-rate

The 'no' variants restore the default behaviour.

Sponsored-by: On-Waves ehf
diff --git a/src/bts.h b/src/bts.h
index 4b7f7e8..ebb7cbf 100644
--- a/src/bts.h
+++ b/src/bts.h
@@ -111,6 +111,10 @@
 struct gprs_rlcmac_bts {
 	uint8_t bsic;
 	uint8_t fc_interval;
+	uint32_t fc_bvc_bucket_size;
+	uint32_t fc_bvc_leak_rate;
+	uint32_t fc_ms_bucket_size;
+	uint32_t fc_ms_leak_rate;
 	uint8_t cs1;
 	uint8_t cs2;
 	uint8_t cs3;