Fix potential double free and use of freed memory in RADIUS client

Fix potential double free and use of freed memory in RADIUS client

ieee802_1x_encapsulate_radius() frees the RADIUS message if
radius_client_send() returns error. This could have resulted in use of
freed memory and double freeing of the RADIUS message if send() fails
since the message is also left in the retransmit list. Avoid this by not
returning error to the caller in such a case.

Signed-off-by: Alexander Couzens <lynxis@c-base.org>