sw test tool: fix pop_pbb action

"The Pop PBB header action does not remove the backbone VLAN
header (B-TAG)" as described in openflow spec 1.3.3.
The format of I-TAG TCI is pcp,..,I-SID,C-DA,C-SA as in
802.1Q-2011 Figure 9-3.

Change the test senario, converting

from B-MAC/I-TAG/S-TAG/C-TAG/ethertype/Data
to   C-MAC/S-TAG/C-TAG/ethertype/Data

looks more common.

Reported-by: Hiroaki KAWAI <kawai@stratosphere.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
of13: support OFPAactionExperimenter with data

The length check assert was added by FUJITA since the spec says that
lenght of data should be a multiple of 8.

Signed-off-by: Rob Udechukwu <rnudechu@ncsu.edu>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>