Create `struct sticky_route'.

Any add' or delete' command that uses MYADDR or HISADDR
will be added to the sticky route list (show ipcp). When
MYADDR or HISADDR change due to IPCP negotiations, and if
`sroutes' is enabled (the default), all sticky route
entries are updated in the routing table.

The end result is that add default hisaddr' will `stick'',
as will ``add myaddr 255.255.255.255 127.0.0.1'' and
``add 1.2.3.4 255.255.255.0 hisaddr''.