msg: fix addr2 encoding for sockaddrs

msg: fix addr2 encoding for sockaddrs

Currently, the sockaddr sa_family field is being sent across the wire
without any sort of endianness conversion.

Redefine the new-style entity_addr_t encoding to encode the sa_family
field as little-endian. This will allow LE machines in the field to
keep limping along, but note that BE machines may break until they are
all fixed.

To do this, use the code that was initially written for BSD/Apple
machines to encode the different fields separately.

Fixes: http://tracker.ceph.com/issues/40114
Signed-off-by: Jeff Layton <jlayton@redhat.com>