tests: net: cm: Increase event wait time

This was seen in CI

START - test_cycle_ready_CC

  Assertion failed at ...tests/net/conn_mgr_monitor/src/main.c:262:
    cycle_ready_ifaces: (stats.conn_count_gen not equal to 1)
    NET_EVENT_L4_CONNECTED should be fired when connectivity is gained.
FAIL - test_cycle_ready_CC in 0.015 seconds

As the event wait timeout is very short (1ms) by default, increase
it to 10ms so that we will not miss the event.

Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>