kernel-netlink: Ensure address changes are not missed in roam events

kernel-netlink: Ensure address changes are not missed in roam events

If multiple roam events are triggered within ROAM_DELAY, only one job is
created.  The old code set the address flag to the value of the last
triggering call.  So if a route change followed an address change within
ROAM_DELAY the address change was missed by the upper layers, e.g. causing
it not to update the list of addresses via MOBIKE.

The new code now keeps the state of the address flag until the job is
actually executed, which still has some issues.  For instance, if an
address disappears and reappears within ROAM_RELAY, the flag would not
have to be set to TRUE.  So address updates might occasionally get
triggered where none would actually be required.

Fixes #374.