After run command `show snmp mib ifmib` and lspci not returned values script crashed
```
lo: ifIndex = 1
ifAlias = lo
ifDescr = lo
eth0: ifIndex = 2
ifAlias = OUTSIDE
Traceback (most recent call last):
File "/usr/libexec/vyos/op_mode/snmp_ifmib.py", line 126, in <module>
print('\t{0}'.format(show_ifdescr(i)))
File "/usr/libexec/vyos/op_mode/snmp_ifmib.py", line 82, in show_ifdescr
vendor = string[3]
IndexError: list index out of range
```
Returned values
```
sudo cat /sys/class/net/eth0/device/vendor
sudo cat /sys/class/net/eth0/device/device
/usr/bin/lspci -mm -d 0x1af4:0x0001
```
needs add additional check