vxlan: trivial indenting fix.

Fix indentation of reserved_flags2 field in vxlanhdr_gpe.

Fixes: e1e5314d ("vxlan: implement GPE")
Signed-off-by: William Tu <u9012063@gmail.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>