Documentation: Clarify that a FileDescriptor must be seekable
Documentation: Clarify that a FileDescriptor must be seekable

In MediaPlayer, methods with an offset specified must be passed a
FileDescriptor that is seekable. This change notes that in the
JavaDoc.

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base