Bluetooth: shell: Fix compile error due to missing memq.h include

Fixes the following compile error when building
tests/bluetooth/shell application:

In file included from subsys/bluetooth/shell/ticker.c:16:0:
subsys/bluetooth/shell/../controller/util/mayfly.h:21:2:
error: unknown type name 'memq_link_t'
  memq_link_t *_link;
  ^~~~~~~~~~~

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>