ns2: count number of dropped packets / bytes on transmit

Differentiate between successfully transmitted packets/bytes,
and pacets/bytes that were dropped (i.e. overflow of net-device)

OsmoNSdummy# show ns nsvc 1001 stats
 NSVCI 01001: UNBLOCKED PERSIST data_weight=1 sig_weight=1 fr)netif: hdlc1 dlci: 1001
  NSVC Peer Statistics:
   Packets at NS Level  ( In):       36 (0/s 8/m 32/h 0/d)
   Packets at NS Level  (Out):    23344 (170/s 20556/m 13119/h 0/d)
   Dropped Packets      (Out):    30692 (230/s 27056/m 17221/h 0/d)
   Bytes at NS Level    ( In):      262 (0/s 24/m 250/h 0/d)
   Bytes at NS Level    (Out): 32741312 (238680/s 28849400/m 18391024/h 0/d)
   Dropped Bytes        (Out): 43014628 (322920/s 37986624/m 24101344/h 0/d)

Change-Id: If21906ff5379038f7be10cf48c68d1f756dd7c1e
diff --git a/src/gb/gprs_ns2_internal.h b/src/gb/gprs_ns2_internal.h
index 68f28db..98b3f29 100644
--- a/src/gb/gprs_ns2_internal.h
+++ b/src/gb/gprs_ns2_internal.h
@@ -88,8 +88,10 @@
 enum ns_ctr {
 	NS_CTR_PKTS_IN,
 	NS_CTR_PKTS_OUT,
+	NS_CTR_PKTS_OUT_DROP,
 	NS_CTR_BYTES_IN,
 	NS_CTR_BYTES_OUT,
+	NS_CTR_BYTES_OUT_DROP,
 	NS_CTR_BLOCKED,
 	NS_CTR_DEAD,
 	NS_CTR_REPLACED,