add test/ifaddrs4096.txt

This file contains enough data for 6 addresses on 4096 fake interfaces.
It should be used to populate a list suitable to return from getifaddrs.
add more test config files for auto-prefix
update ifaddrs4096.txt with more IPv4 addresses
remove test1_auto.conf
test/send.c: split up auto-prefix tests
make addrtostr IPv4 compatible
gram.y, send.c: fix auto-prefix test failures