net: sockev: fix uninitialized data leak into userspace

Socket event string, notifying userspace of socket event, can leak
data into userspace. Memset it before filling it using strlcpy.

Change-Id: I37851f32a1b7ce3307644998c2cc7dd617bb7022
Signed-off-by: Tejaswi Tanikella <tejaswit@codeaurora.org>