Use a pair of ifs when comparing the 32-bit flowid integers so that
the sign bit doesn't cause an overflow. The overflow manifests itself
as a sorting index wrap around in the middle of the sorted array,
which is not a problem for the LRO code, but might be a problem for
the logic inside qsort().

Reviewed by: gnn @
Sponsored by: Mellanox Technologies
Differential Revision: https://reviews.freebsd.org/D5239