examples/l3fwd: fix unaligned memory access on x86

examples/l3fwd: fix unaligned memory access on x86

Fix unaligned memory access when reading IPv6 header which
leads to segmentation fault by changing aligned memory read
to unaligned memory read.

Bugzilla ID: 279
Fixes: 64d3955de1de ("examples/l3fwd: fix ARM build")
Cc: stable@dpdk.org
Signed-off-by: Hariprasad Govindharajan <hariprasad.govindharajan@intel.com>
Reviewed-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>
Reviewed-by: David Christensen <drc@linux.vnet.ibm.com>
Reviewed-by: Herakliusz Lipiec <herakliusz.lipiec@intel.com>
Tested-by: Herakliusz Lipiec <herakliusz.lipiec@intel.com>