Some test scripts use ncat --sctp --listen port to run an SCTP discard

Some test scripts use ncat --sctp --listen port to run an SCTP discard
server in the background. However, when running in the background,
stdin is closed and ncat initiates a graceful shutdown of the SCTP
association. This is not expected by the client. Therefore, the
ncat-based discard server is replaced by a perl-based one.

In addition, to remove the dependency from ncat, which needs to be
installed via the nmap port, also the code testing for a free SCTP port
is changed to use the perl-based client.

Finally, remove some debug output from the report generated.

Reviewed by:		lwhsu@
Differential Revision:	https://reviews.freebsd.org/D20086