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>