test/net: Make sure the tls server socket is accepting before connect

Client thread might run before the server gets to put itself on accept.
Leading to the server waiting forever.

Signed-off-by: Tomasz Bursztyka <tomasz.bursztyka@linux.intel.com>
diff --git a/tests/net/socket/tls/src/main.c b/tests/net/socket/tls/src/main.c
index 8309bc2..5aa9bdf 100644
--- a/tests/net/socket/tls/src/main.c
+++ b/tests/net/socket/tls/src/main.c
@@ -24,7 +24,6 @@
 #define MAX_CONNS 5
 
 #define TCP_TEARDOWN_TIMEOUT K_SECONDS(1)
-#define THREAD_SLEEP 50 /* ms */
 
 static const unsigned char psk[] = {
 	0x01, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
@@ -72,13 +71,15 @@
 
 static void test_connect(int sock, struct sockaddr *addr, socklen_t addrlen)
 {
+	k_yield();
+
 	zassert_equal(connect(sock, addr, addrlen),
 		      0,
 		      "connect failed");
 
 	if (IS_ENABLED(CONFIG_NET_TC_THREAD_PREEMPTIVE)) {
 		/* Let the connection proceed */
-		k_msleep(THREAD_SLEEP);
+		k_yield();
 	}
 }