net: mctp: mctp_test_route_extaddr_input cleanup

The sock was not being released. Other than leaking, the stale socket
will conflict with subsequent bind() calls in unrelated MCTP tests.

Fixes: 46ee1646 ("net: mctp: test: Add extaddr routing output test")
Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
Link: https://patch.msgid.link/20250710-mctp-bind-v4-1-8ec2f6460c56@codeconstruct.com.au


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