iproute: support for filtering by and printing of scope

iproute: support for filtering by and printing of scope

This patch adds filtering by and printing of 'scope' to the
ip route command, taken from the upstream ip command.

x86_64:
function                                             old     new   delta
iproute_list_or_flush                               1548    1674    +126
print_route                                         2394    2469     +75
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 201/0)             Total: 201 bytes

mipsel:
iproute_list_or_flush                               1952    2096    +144
print_route                                         2580    2696    +116
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 2/0 up/down: 260/0)             Total: 260 bytes

Signed-off-by: André Draszik <git@andred.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>