Verify that udpgso can generate segments smaller than device mtu, down
to the extreme case of 1B gso_size.

Verify that irrespective of gso_size, udpgso restricts the number of
segments it will generate per call (UDP_MAX_SEGMENTS).
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Corked sockets take a different path to construct a udp datagram than
the lockless fast path. Test this alternate path.
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Connected sockets use path mtu instead of device mtu.

Test this path by inserting a route mtu that is lower than the device
mtu. Verify that the path mtu for the connection matches this lower
number, then run the same test as in the connectionless case.
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Validate udp gso, including edge cases (such as min/max gso sizes).
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>