Revert "Hide ipv6_dhcp_lifetime when Auto Configuration is set to Stateless"

This reverts commit 2e4afc10916805e7299d3151cfe604a68225c189.
Revert "Make functions static as they must be called inside notify_rc"

This reverts commit 7324836d3048541322a66abaa7082ea471134475.
Revert "SIGHUP causes radvd to terminate"

This reverts commit 12e3ad461a159bd48a5343a1b4c54ac99fadd64f.
Revert "Do not restart radvd if config is updated"

This reverts commit 4a549e0306c3e48966138c638422b556fc6e4554.