uncut_bits: comment
fix crashes with non openflow_basic match fields
change oxm on-wire length for ipv6_flabel and mpls_label

this is doubtful per spec but matches with ONF openflow.h and
other implementations.  (ovs, ryu, ...)
Fix incorrect github urls. Closes  FlowForwarding/LINC-Switch#271
Merge pull request #57 from yamt/oxm-4bytes

make oxm on-wire length for ipv6_flabel and mpls_label 32-bit
Merge remote-tracking branch 'refs/remotes/origin/master' into v5
Apply changes from master branch to ofp_v5

The changes were originally made in the following commits:

- ddd6dffc700bbb3379a5d0822d2feb8c4764280c
- 202a5afc27ed2aad3c9367ed022d119f23592e38