it is not recommended to do so, but this is how i did it
# ipadm show-addr
#ipadm delete-addr vnic3/v6
#ipadm show-addr
#ipadm delete-addr lo0/v6
#ipadm show-addr
#svcadm disable svc:/network/routing/legacy-routing:ipv6
#svcadm disable svc:/network/dhcp/server:ipv6
#svcadm disable svc:/network/dhcp/relay:ipv6