/*
* Resolve an IP address into an ethernet address. If success,
* desten is filled in. If there is no entry in arptab,
* set one up and broadcast a request for the IP address.
* Hold onto this mbuf and resend it once the address
* is finally resolved. A return value of 0 indicates
* that desten has been filled in and the packet should be sent
* normally; a return value of EWOULDBLOCK indicates that the packet has been
* held pending resolution.
* Any other value indicates an error.
*/