[BUG] ipdevinfo ip search crashes on invalid IP address input

[lunkwill42]

Describe the bug

If the view portadmin-ip is visited using an invalid IP address as input, the page crashes with a TypeError, rather than handle the error gracefully. This also results in an e-mail being sent unnecessarily to the site admins.

It's not clear how this URL is reachable from within NAV. It may be that someone edited a URL by hand and made a typo, provoking this silly error.

To Reproduce

1. Go to /ipdevinfo/ip=127.0.0.256/ on your NAV installation.
2. See error

Expected behavior

If the IP input is invalid, the page should render normally, but display a helpful error message to that effect.

Tracebacks

Traceback (most recent call last):
  File "/opt/venvs/nav/lib/python3.7/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/opt/venvs/nav/lib/python3.7/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/web/ipdevinfo/views.py", line 271, in ipdev_details
    netbox = get_netbox(name=name, addr=addr)
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/web/ipdevinfo/views.py", line 177, in get_netbox
    host_information = get_host_info(name or addr)
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/web/ipdevinfo/host_information.py", line 51, in _get_host_info
    if is_valid_ip(host, strict=True):
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/util.py", line 80, in is_valid_ip
    return _is_valid_ip_socket(ip)
  File "/opt/venvs/nav/lib/python3.7/site-packages/nav/util.py", line 88, in _is_valid_ip_socket
    socket.inet_pton(socket.AF_INET, ip)  # IPv4

Environment (please complete the following information):

• NAV version installed: 5.6.0

[lunkwill42]

Fixed by #2590