ANDROID: af_unix: Provide ABI fixes for recently introduced 'struct scm_fp_list' attribute 'dead'

Adding new attributes to the ABI protected 'struct scm_fp_list' changes
the offsets of the fields already present in the structure which could
cause issues if modules already have a copy and are unaware of the
changes.  Let's add it to the end of the structure, under the protection
of __GENKSYMS__ as is SOP.

Bug: 404256079
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: If926b8a8bbf293304bbeb7cba66cafe158381fa6