I ran into a bug today related to how Linux handles a route's nexthop
flags when there is just one nexthop. Namely Linux expects the flags
to be OR'd into the rtm_flags field when there is only one nexthop and
so rtnl_route_build_msg needs to check the number of nexthops and
store the nexthops flags into this field prior to calling
nlmsg_append(...&rtmsg).
Conversely the rtnl_route_parse function needs to pull these lower
0xff bits when a single nexthop is detected.
Attached is my patch. I don't like the slight duplication of doing
the rtnl_route_get_nnexthops check twice but it seemed to be the least
turmoil of any solution I thought of.
b62e019afa