Count forwarded packet
ipmib.ForwDatagrams
skb
pointer to the struct sk_buff being acted on
op
value to be added to the counter (default value of 1)
The packet pointed to by skb is filtered by the function ipmib_filter_key. If the packet passes the filter is is counted in the global ForwDatagrams (equivalent to SNMP's MIB IPSTATS_MIB_OUTFORWDATAGRAMS)