in_pcb: limit the effect of wraparound in TCP random port allocation check
The check to see if TCP port allocation should change from random to sequential port allocation mode may incorrectly cause a false positive due to negative wraparound. Example: V_ipport_tcpallocs = 2147483585 (0x7fffffc1) V_ipport_tcplastcount = 2147483553 (0x7fffffa1) V_ipport_randomcps = 100 The original code would compare (2147483585 <= -2147483643) and thus incorrectly move to sequential allocation mode. Compute the delta first before comparing against the desired limit to limit the wraparound effect (since tcplastcount is always a snapshot of a previous tcpallocs).
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