src: Use memcpy() to handle potentially unaligned data

src: Use memcpy() to handle potentially unaligned data

Rolf Eike Beer <eike@sf-mail.de> reported that nft-expr_quota-test fails
with a SIGBUS on SPARC due to unaligned accesses. This patch resolves
that and fixes additional sources of unaligned accesses matching the
same pattern. Both nft-expr_quota-test and nft-expr_objref-test
generated unaligned accesses on DEC Alpha.

Bug: https://bugs.gentoo.org/666448
Signed-off-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>