net: sockev: code cleanup

Replace with cleaner NULL checks. Needed for dependent change
commit 59f6fd5f1905 ("net: core: null pointer derefernce in
		sockev_client_cb").

Change-Id: Icdd7a5c9f3e3f343bb20b1f9b75fa580ea75a2dc
Signed-off-by: Tejaswi Tanikella <tejaswit@codeaurora.org>