Add custom prefix functionality for netlab if_link
I needed specific prefix for if_link so I extended netlab's functionality.
If there is /
present in the prefix it will not add the default /24
prefix.
Example:
if_net net1
if_link rs_ipv4 ve0 net1 193.203.0.251/16
if_link n42x357 ve0 net1 193.203.0.33
In the first case the default /24
is not added but in the second one it is.