Reimplement the max-transfer-time-out and max-transfer-idle-out

While refactoring the libns to use the new network manager, the max-transfer-*-out options were not implemented and they were turned non-operational.

Reimplement the max-transfer-idle-out functionality using the write timer and max-transfer-time-out using the new isc_nm_timer API.

Closes #1897 (closed)