[rt27912]
Add code to suppor on {commit expiry release} statements for DHCPv6.
There are several pieces to this change
1) Add space in the iasubopt structure to hold the statement pointers
2) Update the execute code to fill in the structures as necessary
3) Execute the statements when appropriate
Many of the changes in the non-v6 code are to pass the v6 structures
around to the execute code.
