Fix several bugs in r297374:

• fix UP build [1]
• do not obliterate initial reading of rdtsc by the loop counter [2]
• restore the meaning of the argument -1 to native_lapic_ipi_wait() as wait until LAPIC acknowledge without timeout
• correct formula for calculating loop iteration count for 1us, it was inverted, and ensure that even on unlikely slow CPUs at least one check for ack is performed.

Reported by: Michael Butler <imb@protected-networks.net> [1], rpokala[2],
jhb[3]
Tested by: Michael Butler
Pointy hat to: kib
Sponsored by: The FreeBSD Foundation