MFC: r311817

MFC: r311817

In dummynet(4), random chunks of memory are casted to struct dn_*,
potentially leading to fatal unaligned accesses on architectures with
strict alignment requirements. This change fixes dummynet(4) as far
as accesses to 64-bit members of struct dn_* are concerned, tripping
up on sparc64 with accesses to 32-bit members happening to be correctly
aligned there. In other words, this only fixes the tip of the iceberg;
larger parts of dummynet(4) still need to be rewritten in order to
properly work on all of !x86.
In principle, considering the amount of code in dummynet(4) that needs
this erroneous pattern corrected, an acceptable workaround would be to
declare all struct dn_* packed, forcing compilers to do byte-accesses
as a side-effect. However, given that the structs in question aren't
laid out well either, this would break ABI/KBI.
While at it, replace all existing bcopy(9) calls with memcpy(9) for
performance reasons, as there is no need to check for overlap in these
cases.

PR:		189219

git-svn-id: svn://svn.freebsd.org/base/stable/10@318155 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f