Paclen restrictions are not exposed

[thombles]

For example when you define a radio in /etc/ax25/axports there is a paclen parameter.

paclen - is the default maximum packet size for this interface.

man page

If you try to transmit packets greater than this length then it will fail (at least in my previous testing). The linuxif TNC (and any others that work similarly) should query this information and make it available on the Tnc so the application can perform appropriate fragmentation.