OSPFd: Clean up Segment Routing patch

OSPFd: Clean up Segment Routing patch

 - ospfd/ospf_te.c: Remove unregister function and call to
ospf_delete_opaque_functab() following the introduction of
ospf_opaque_term() function in ospfd.c for ospfd termination.
 - ospfd/ospf_sr.c: Set initial index value for node-msd CLI to
avaoid crash when using this command
 - ospfd/ospf_ext.c: Disable call to ospf_sr_update_prefix() if
Segment Routing, thus Extended Link/Prefix, is not enable
 - ospfd/ospf_opaque.c: Correct scheduling of Opaque LSA flooding

Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>