Every so often I get concerned because OVS does most of its time arithmetic
in "long long int" but poll_timer_wait() takes an "int", so there is
potential for truncating a large value to a small value or a positive value
to a negative value. That would cause excessive wakeups and possibly 100%
CPU usage.
This commit therefore changes poll_timer_wait()'s parameter type from "int"
to "long long int". The file-scope 'timeout' variable remains type "int"
because that is the type of poll()'s timeout argument.
Factoring poll_timer_wait() into two functions is not necessary here but it
comes in handy in the following patch.
