Revert "neighbour: fix unaligned access to pneigh_entry"

This reverts commit 7e0da73c which is
commit ed779fe4.

It breaks the Android kernel ABI, and is not needed for Android systems,
so it is safe to revert.

Bug: 161946584
Change-Id: I415d35f983e65c2ce732f1089861e80990d63451
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>