tui: adjust tests for guessing address prefix
Since NetworkManager commit 08d7bf5988173f8569b17c646eb1a5c5d9d9340c, rh#1474295, nmtui guesses the address prefix for RFC1918 private addresses and uses by default a /64 prefix for IPv6 addresses.
Fix tests @nmtui_ipv4_addresses_static_no_mask
and @nmtui_ipv6_addresses_static_no_mask
for master.