Fix SocketKeepalive APIs which do not meet API review requirement

Per API review, change the use of FileDescriptor to
ParcelFileDescriptor.
This change also fix nullability according to API review
feedbacks.

Fix: 126698610
Fix: 126699425
Fix: 126699232
Fix: 126700278

Test: 1. m -j
      2. atest FrameworksNetTests --generate-new-metrics 50
      3. m -j doc-comment-check-docs
Change-Id: I19476c50dd1ca290bf3f41973829da2bd229796a