Fix overflows in intermediate calculations in sysctl_msec_to_ticks(). At hz values of 1000 and above the overflows caused net.inet.tcp.keepidle to be reported as negative.
Fix overflows in intermediate calculations in sysctl_msec_to_ticks().
At hz values of 1000 and above the overflows caused net.inet.tcp.keepidle
to be reported as negative.

MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase