mod_manager truncates ENABLE-APP messages

With lots of aliases, ENABLE-APP messages can be big enough to span several IP packets.
Sometimes, mod_manager will read only the first packet.
The message is therefore incomplete and mod_cluster configuration ends up corrupted : some aliases are missing and the context-root is replaced by "/".

This is caused by a wrong usage of ap_get_brigade() : it's called only once whereas it should be called until there's nothing left to read (see the attached patch).