support UDP drops #506
Description
on newer linux systems /proc/net/udp (and /proc/net/udp6) have a drop column on the far right:
$ uname -a
Linux ip-172-31-10-56 5.4.0-1045-aws #47~18.04.1-Ubuntu SMP Tue Apr 13 15:58:14 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
$ cat /proc/net/udp
sl local_address rem_address st tx_queue rx_queue tr tm->when retrnsmt uid timeout inode ref pointer drops
4000: 3500007F:0035 00000000:0000 07 00000000:00000000 00:00000000 00000000 101 0 256693 2 0000000000000000 0
4015: 380A1FAC:0044 00000000:0000 07 00000000:00000000 00:00000000 00000000 100 0 1016179 2 0000000000000000 0
5890: 0100007F:8797 0100007F:C351 01 00000000:00000000 00:00000000 00000000 1001 0 1016395 2 0000000000000000 0
8736: 00000000:12B5 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 32052 2 0000000000000000 0
12419: 00000000:2118 00000000:0000 07 00000000:00000000 00:00000000 00000000 0 0 24157 2 0000000000000000 0