msg/msg_types: fix the entity_addr_t's decoder

msg/msg_types: fix the entity_addr_t's decoder

the daemon is vulnerable to malicious client, which is able to send
large elen, and corrupt the stack, etc.

* throw at seeing corrupted entity_addr_t where its elen exceeds
  the length of sockaddr
* handle the exception thrown when decoding entity_addr_t in messenger
  layer.
* if a malicious client manages to send a corrutped entity_addr_t to
  daemon, daemon will crash because decode fails and the exception is
  not handled. it's better than continuing working with the bogus
  message.

Signed-off-by: Kefu Chai <kchai@redhat.com>