VPP check ethernet interface exist before adding to vpp
```
set vpp settings interface eth99 driver dpdk
```
commit:
```
vyos@r14# commit
[ vpp ]
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/vyos/vpp/utils.py", line 251, in __init__
ioctl(sockfd, SIOCETHTOOL, ifreq)
OSError: [Errno 19] No such device
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/libexec/vyos/services/vyos-configd", line 136, in run_script
c = script.get_config(config)
^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/libexec/vyos//conf_mode/vpp.py", line 152, in get_config
EthtoolGDrvinfo(iface).driver
^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3/dist-packages/vyos/vpp/utils.py", line 253, in __init__
raise FileNotFoundError(f'There is no Ethernet device: {iface}')
FileNotFoundError: There is no Ethernet device: eth99
[[vpp]] failed
Commit failed
[edit]
vyos@r14#
```