Added support to alias interfaces (e.g., ifname0:1)

[pdcleyn]

In linux, alias interfaces can end up in /proc/net/dev as shown below:

[root@host ~]# cat /proc/net/dev
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
    lo: 1638928809 4771634    0    0    0     0          0         0 1638928809 4771634    0    0    0     0       0          0
  eth0: 1000866899965 764654426    0    0    0     0          0         0 1267144066 5373060    0    0    0     0       0          0
tun999999:       0       0    0    0    0     0          0         0        0       0    0   15    0     0       0          0
tun10001:1:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0
tun10001:2:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          

Current parsing will delimit field on a : only which results in :1 as the first element of a line with an alias interface. This will result in an error as :1 will not be parseable to an int later on.

This PR changes the delimiter to : (space added), correctly parsing alias interfaces as well.

[pdcleyn]

This issue causes telegraf to fail. I create an issue on the telegraf project for this and referred to this PR.

[shirou]

Thank you for reporting. I did not aware like tun10:1: