libs/ipv6-uipbuf

This example is meant to showcase the capabilities of uipbuf. It currently focuses only on UIPBUF_ATTR_MAX_MAC_TRANSMISSIONS, which lets an application set a custom max number of MAC transmissions. Optionally, this information can be passed on over multiple hops, so that the attribute applies along the full path. This requires setting UIP_CONF_TAG_TC_WITH_VARIABLE_RETRANSMISSIONS.