vxlan: fix duplicated and wrong error messages

vxlan_dev_configure outputs error messages before returning, no need to
print again the same mesages in vxlan_newlink. Also, vxlan_dev_configure may
return a particular error code for a different reason than vxlan_newlink
thinks.

Move the remaining error messages into vxlan_dev_configure and let
vxlan_newlink just pass on the error code.

Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>