Split the network and netmask into separate terms and sort on netmask within network.

knoppix@Microknoppix:~$ perl -MSocket -Mstrict -wE '
my @networks = qw{
   10.182.8.0/26
   10.182.8.0/21
   10.182.8.64/26
   10.182.8.128/26
   10.182.8.192/26
   };

say for
   map  { $_->[ 0 ] }
   sort { $a->[ 1 ] cmp $b->[ 1 ] || $a->[ 2 ] <=> $b->[ 2 ] }
   map  { my( $network, $netmask ) = split m{/};
          [ $_, inet_aton( $network ), $netmask ];
        }
   @networks;'
10.182.8.0/21
10.182.8.0/26
10.182.8.64/26
10.182.8.128/26
10.182.8.192/26
knoppix@Microknoppix:~$
[download]

I hope this is helpful.