coap_io.c: set send address when IP_PKTINFO is missing
coap_io.c: set send address when IP_PKTINFO is missing

Try IP_SENDSRCADDR to set the address of the sending interface for
sendmsg() on platforms that do not provide IP_PKTINFO (such as
FreeBSD).

authmillenon/libcoap,authmillenon/libcoap,authmillenon/libcoap