syslogd: make "reopen log file every second" logic work for multiple logs

Move last_log_time from a single global to *each logFile_t*
so that we can actually apply the logic to every log-file
in multi-file configurations, rather than working only
for the first file written in each 1-second interval
and then leaving the others connected to possibly wrong files.

Signed-off-by: Joshua Judson Rosen <jrosen@harvestai.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>