aodvv2: do not declare public aodv_get_next_hop static
aodvv2: eliminate warnings for unused parameters

These parameter are required for compatibility to oonf_api.
aodvv2: removed unused parameter from _get_link_cost
aodvv2: eliminated unused parameter hoplimit
aodvv2: eliminated debug induced warning
aodvv2: fixed thread entry function prototypes
Turn all variables denoting the number of unreachable nodes into size_t

This is an extension of Oleg's 3912b34822