Adds a check to each IPFIX set ID branch, checking if the rest of the
bytes in this set is padding/zeroes.

Refs #34

…g field length in template.

Signed-off-by: Khaw Teng Kang <tk.khaw@attrelogix.com>

Refs #34

Tested implementation of IPFIX set padding handling. Uses TK-Khaw's
proposed no_padding_last_offset calculation, extended as modulo
calculation to match multiple data set records.

Tests were conducted by capturing live traffic on a test machine with
tcpdump, then this capture file was read in by softflowd 1.1.0, with the
collector.py as the export target. The exported IPFIX (v10) packets were
then using both no padding and padding, so that tests could be
validated.

Closes #34

Signed-off-by: Dominik Pataky <software+pynetflow@dpataky.eu>

Adds another check when parsing a set. The check "offset !=
self.header.length" allows to skip the padding checks if the offset is
the same as the length, not calling rest_is_padding_zeroes and wasting
CPU time.