packet/zebra: Support asymmetric structure of ZEBRA_*_IMPORT_LOOKUP
packet/zebra: Support asymmetric structure of ZEBRA_*_IMPORT_LOOKUP

The ZEBRA_IPV4_IMPORT_LOOKUP/ZEBRA_IPV6_IMPORT_LOOKUP has asymmetric
structures at when sent to Zebra daemon and when sent from Zebra daemon.
Especially, "prefix_len" field is inserted before "prefix" filed when
sent to Zebra daemon.

Signed-off-by: IWASE Yusuke <bb80e84cc9f5a8f01385872ee89032beb5d4eba7@gmail.com>
Signed-off-by: FUJITA Tomonori <93dac1fe9c4b2a3957982200319981492ad4976e@lab.ntt.co.jp>

fujita/ryu,iwaseyusuke/ryu,osrg/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,osrg/ryu,osrg/ryu,iwaseyusuke/ryu,fujita/ryu,fujita/ryu,lagopus/ryu-lagopus-ext,iwaseyusuke/ryu,iwaseyusuke/ryu,lagopus/ryu-lagopus-ext,fujita/ryu,osrg/ryu,osrg/ryu,lagopus/ryu-lagopus-ext,lagopus/ryu-lagopus-ext