docs: Update MessageAPI notes to mention the unreliable transmission nature.
docs: Update MessageAPI notes to mention the unreliable transmission nature.

Bug: 17527501
Change-Id: I385747e4453c5079d7a034fbe7377a5fb260fa1d

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