fix flags printing tests

The test cases included the timestamp (due to missing -t) and failed
unless run in the same timezone as produced. The failures printed by
print-flags.sh did not make it into the final report because the script
always returned 0.

Strip the timestamps and replace print-flags.sh with some contents in
TESTLIST.
fix printing of unknown TCP options

TCP options decoder would mix decimal and hexadecimal digits when
printing an unknown option. For example, the pre-TFO revision would
print TFO as follows:
[Unknown Option 254f989090909090000]

Refine output format to print the same data as follows:
[unknown-254 0xf989090909090000]