net: ipv6: ioam6: fix lwtunnel_output() loop

Fix the lwtunnel_output() reentry loop in ioam6_iptunnel when the
destination is the same after transformation. Note that a check on the
destination address was already performed, but it was not enough. This
is the example of a lwtunnel user taking care of loops without relying
only on the last resort detection offered by lwtunnel.

Fixes: 8cb3bf8b ("ipv6: ioam: Add support for the ip6ip6 encapsulation")
Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
Link: https://patch.msgid.link/20250314120048.12569-3-justin.iurman@uliege.be


Signed-off-by: Paolo Abeni <pabeni@redhat.com>