ipcalc command doesn’t work for ipv6

Issue

• The ipcalc command doesn’t work for ipv6
• Ipcalc does not support ipv6

$ ipcalc -6 --network 2607:f8b0:4006:801::1009/128
ipcalc: unable to show setting for IPv6

• Does not report error with invalid prefix, e.g. x1

$ipcalc -6c 2607:f8b0:4006:801::1009/x1
$ echo $?
0