bsd: Prepare event buffer on init process

bsd: Prepare event buffer on init process

Currently these three steps runs for each event.
1. get buffer size via system
2. allocate a memory for event
3. free the memory

The wpa_supplicant receives 4 events from boot to be connected.
So this patch prepare the event buffer at the init process.

I have tested wpa_supplicant on NetBSD 6.1.2.
But I could not tested hostapd because I do not have AP enabled device.

Signed-hostap: Masashi Honma <masashi.honma@gmail.com>