Improve TCP related tests for dtrace.
Ensure that the TCP connections are terminated gracefully as expected
by the test. Use appropriate numbers for sent/received packets.
In addition, enable tst.localtcpstate.ksh, which should pass, but
doesn't until https://reviews.freebsd.org/D16369 is committed.
Reviewed by: markj@
Sponsored by: Netflix, Inc.
Differential Revision: https://reviews.freebsd.org/D16288