nl_l3: properly check if ip addresses should be applied
nl_l3: properly check if ip addresses should be applied

Use the new function to find out if an ip address is on a switch
interface, and only apply it in this case.

This also fixes IPv6 link local entries appearing when IPv6 link local
addresses are added for foreign interfaces like the management
interface.

Signed-off-by: Jonas Gorski <9712c064bde5a52658fc87d6454b4956f9bf286b@bisdn.de>

bisdn/basebox,bisdn/basebox,bisdn/basebox,bisdn/basebox