Split rtrequest1_fib() into smaller manageable chunks.

[melifaro]

Summary

No functional changes.

Move route addition / route deletion code from rtrequest1_fib()

to add_route() and del_route() respectively.

Rename rtrequest1_fib_change() to change_route() for consistency.
Shrink the scope of ugly info #defines.

Test Plan

test_rtsock_l3:rtm_add_v4_gu_ifa_ordered_success  ->  passed  [0.135s]
test_rtsock_l3:rtm_add_v4_gw_direct_success  ->  passed  [0.125s]
test_rtsock_l3:rtm_add_v4_temporal1_success  ->  passed  [0.136s]
test_rtsock_l3:rtm_add_v6_gu_gw_gu_direct_success  ->  passed  [0.118s]
test_rtsock_l3:rtm_add_v6_gu_ifa_hostroute_success  ->  passed  [0.121s]
test_rtsock_l3:rtm_add_v6_gu_ifa_ordered_success  ->  passed  [0.115s]
test_rtsock_l3:rtm_add_v6_gu_ifa_prefixroute_success  ->  passed  [0.116s]
test_rtsock_l3:rtm_add_v6_temporal1_success  ->  passed  [0.115s]
test_rtsock_l3:rtm_change_v4_gw_success  ->  passed  [0.121s]
test_rtsock_l3:rtm_change_v4_mtu_success  ->  passed  [0.115s]
test_rtsock_l3:rtm_change_v6_gw_success  ->  passed  [0.146s]
test_rtsock_l3:rtm_change_v6_mtu_success  ->  passed  [0.113s]
test_rtsock_l3:rtm_del_v4_gu_ifa_prefixroute_success  ->  passed  [0.117s]
test_rtsock_l3:rtm_del_v4_prefix_nogw_success  ->  passed  [0.116s]
test_rtsock_l3:rtm_del_v6_gu_ifa_hostroute_success  ->  passed  [0.117s]
test_rtsock_l3:rtm_del_v6_gu_ifa_prefixroute_success  ->  passed  [0.118s]
test_rtsock_l3:rtm_del_v6_gu_prefix_nogw_success  ->  passed  [0.116s]
test_rtsock_l3:rtm_get_v4_empty_dst_failure  ->  passed  [0.002s]
test_rtsock_l3:rtm_get_v4_exact_success  ->  passed  [0.141s]
test_rtsock_l3:rtm_get_v4_hostbits_failure  ->  passed  [0.120s]
test_rtsock_l3:rtm_get_v4_lpm_success  ->  passed  [0.119s]
test_rtsock_lladdr:rtm_add_v4_gu_lle_success  ->  passed  [0.124s]
test_rtsock_lladdr:rtm_add_v6_gu_lle_success  ->  passed  [0.117s]
test_rtsock_lladdr:rtm_add_v6_ll_lle_success  ->  passed  [0.114s]
test_rtsock_lladdr:rtm_del_v4_gu_lle_success  ->  passed  [0.119s]
test_rtsock_lladdr:rtm_del_v6_gu_lle_success  ->  passed  [0.124s]
test_rtsock_lladdr:rtm_del_v6_ll_lle_success  ->  passed  [0.112s]