ipa_keepalive_fsm: Fix OSMO_IPA_KA_E_STOP allstate event

We had the allstate_action function registered, and that function
implemented handling of OSMO_IPA_KA_E_STOP.  However, the
allstate_event_mask was not set, rendering this functionality
inaccessible.

Change-Id: I83fd991bdacb7bab794878e47c7797fecf8b9286
diff --git a/src/input/ipa_keepalive.c b/src/input/ipa_keepalive.c
index 1aae096..6467720 100644
--- a/src/input/ipa_keepalive.c
+++ b/src/input/ipa_keepalive.c
@@ -189,6 +189,7 @@
 	.states = ipa_keepalive_states,
 	.num_states = ARRAY_SIZE(ipa_keepalive_states),
 	.log_subsys = DLINP,
+	.allstate_event_mask = S(OSMO_IPA_KA_E_STOP),
 	.allstate_action = ipa_ka_allstate_action,
 	.event_names = ipa_keepalive_event_names,
 	.timer_cb = ipa_ka_fsm_timer_cb,