net/enc28j60: oops fix

Prevent oops on enc28j60 packet RX:  make sure buffers are aligned.
Not all architectures support unaligned accesses in kernel space.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Claudio Lanconelli <lanconelli.claudio@eptar.com>
Signed-off-by: David S. Miller <davem@davemloft.net>