trailing whitespace & indentation

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
add a bit fat comment for short but non trivial
int can_decrease_mask(const struct subnet *s);

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
add comment for non trivial subnet_remove

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
modify usage() (better ordering)

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
add a 'remove' command

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
update regtest for "subnet remove"

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
clean up the subnet strng in remove subnet (first_ip)

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
we are not barbarians; free what we alloced, even if we have to exit

Signed-off-by: etienne basset <etienne.basset@numericable.fr>
create a remove_subnet_file

Signed-off-by: etienne basset <etienne.basset@numericable.fr>