net/vxlan: Fix kernel unaligned access in __vxlan_find_mac

__vxlan_find_mac invokes ether_addr_equal on the eth_addr field,
which triggers unaligned access messages, so rearrange vxlan_fdb
to avoid this in the most non-intrusive way.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Reviewed-by: Jiri Pirko <jiri@resnulli.us>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>