ifconfig: Pacify a sign comparison warning in regdomain_sort.

[jhb]

Summary

Both ic_flags values are unsigned (uint32_t), so cast them to a signed
int to generate a signed result. Both ic_req values are also
unsigned, but since they are uint16_t, they are implicitly promited to
int before the subtraction.

Reported by: GCC -Wsign-compare

[emaste]

I think this is fine and suspect that the actual order is not that important, but I wonder if it would be more clear to make it explicit?

something like

if (ca->ic_freq > cb->ic_freq)
        return 1;
else if (ca->ic_freq < cb->ic_freq)
        return -1;
else if (ca->ic_flags & CHAN_ALL > cb->ic_flags & CHAN_ALL)
...

(signs might be backwards)

[jhb]

I almost did a broken out version like that, but it is a fair bit more verbose.