ip rule: unify parsing args

ip rule: unify parsing args

function                                             old     new   delta
do_iprule                                             83     134     +51
print_rule                                           736     726     -10
iprule_list                                           73       -     -73
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 1/1 up/down: 51/-83)            Total: -32 bytes

Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>