afsocket: fix transport-mapper-unix to contain the proper source file

transport-mapper-unix was actually a duplicate of transport-mapper-inet
due to a typo in the Makefile.
afsocket: added assert_transport_mapper_apply_fails() to transport-mapper-lib

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>
afsocket: build test programs with SSL enabled
afsocket: delegate LogTransport factory function to TransportMapper instance
afsocket: remove construct_transport() in favour of TransportMapper->construct_log_transport

Instead of overriding construct_transport in the driver classes to create a
LogTransportTLS, fully delegate LogTransport creation to TransportMapper.

This means that tls_context and related functions have also moved to
TransportMapper and were removed from the driver classes.

Signed-off-by: Balazs Scheidler <bazsi@balabit.hu>