qapi event: convert SPICE events

qapi event: convert SPICE events

SPICE_INITIALIZED, SPICE_CONNECTED, SPICE_DISCONNECTED and
SPICE_MIGRATE_COMPLETED are converted in one patch, since they
use some common functions. inet_strfamily() is removed since no
callers exist anymore.

Note that there is no existing doc for SPICE_MIGRATE_COMPLETED
in docs/qmp/qmp-events.txt before this patch.

Signed-off-by: Wenchao Xia <wenchaoqemu@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>