gram.y: move auto-select prefix logging
send.c: cleanup, add logging in auto-prefix code
test/send.c: improve auto-prefix tests
test/send.c: fix getaddrs not returning a value

this also changes the ipv6 addresses a bit.
send.c: swap bytes in test get_v4addr
send.c: push iface->prefix loop down a level in auto-prefix code
test/send.c: fix mask and next pointers in struct ifaddrs
send.c: tune loops to be lazy

Before looping, do the fasted checks first to ensure the laziest condition
checking before doing any real work.
test/send.c: make ifaddrs names dynamic