Modify dl_list_for_each() to not use unaligned access with WPA_TRACE

Modify dl_list_for_each() to not use unaligned access with WPA_TRACE

UBSan testing with WPA_TRACE=y ended up hitting an unaligned access for
struct os_alloc_trace in os_program_deinit() because of the
dl_list_for_each() design that looked like dereferencing the member
element of the list head which is something that does not exist.

Get the first entry from the list using dl_list_first() so that the
empty list special case is covefred and compare item pointers instead of
struct dl_list pointers to check whether the end of the loop has been
reached.

Signed-off-by: Jouni Malinen <j@w1.fi>