gpsr_ns2_udp: Use osmo_io_fd instead of osmo_fd

Change-Id: Id776d2d9f35c304620f3d5b94492148dd987f5a0
diff --git a/src/gb/gprs_ns2_internal.h b/src/gb/gprs_ns2_internal.h
index 4f33221..37b142e 100644
--- a/src/gb/gprs_ns2_internal.h
+++ b/src/gb/gprs_ns2_internal.h
@@ -6,6 +6,7 @@
 #include <stdint.h>
 
 #include <osmocom/core/logging.h>
+#include <osmocom/core/rate_ctr.h>
 #include <osmocom/gprs/protocol/gsm_08_16.h>
 #include <osmocom/gprs/gprs_ns2.h>