Make debug msg about fsm timeout more obvious

Signed-off-by: Olaf Hering <olaf@aepfle.de>
make ni_dhcp4_fsm_set_timeout_msec static

Signed-off-by: Olaf Hering <olaf@aepfle.de>
make ni_dhcp4_fsm_set_timeout static

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Adjust comment in ni_timer_get_time about the need for wallclock time

Signed-off-by: Olaf Hering <olaf@aepfle.de>