vrf: T8320: only allow alpha numerical characters, - and _ as VRF name

This prevents the Kernel to error out. VRF names are limited within the Linux
kernal as any other network interface name. See net/core/dev.c:dev_valid_name()!

vyos@vyos# set vrf name MGM>T table 1000
vyos@vyos# commit
[ vrf ]
Traceback (most recent call last):
  File "/usr/libexec/vyos/services/vyos-configd", line 157, in run_script
    script.apply(c)
  File "/usr/libexec/vyos/conf_mode/vrf.py", line 317, in apply
    vrf_if.add_addr('127.0.0.1/8')
  File "/usr/lib/python3/dist-packages/vyos/ifconfig/interface.py", line 1294, in add_addr
    elif not is_intf_addr_assigned(self.ifname, addr, netns=netns):
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/vyos/utils/network.py", line 444, in is_intf_addr_assigned
    json_out = json.loads(out)
               ^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

[[vrf]] failed
Commit failed

0 files changed, 0 insertions, 0 deletions