ipa_keepalive_fsm: Suppress error messages for INIT -> INIT transition

If we receive an OSMO_IPA_KA_E_STOP in INIT state, we are trying to
re-enter INIT, which is not permitted as per the FSM definition.

Adding this permission avoids the below error message from hitting the
logs every time this happens:

<0003> input/ipa_keepalive.c:158 IPA-KEEPALIVE(server)[0x612000000520]{INIT}: transition to state INIT not permitted!

Change-Id: I8db2f2e708fc4fbb81f5019973098a80e8f540d2

src/input/ipa_keepalive.c

@@ -167,7 +167,7 @@ static const struct osmo_fsm_state ipa_keepalive_states[] = {
 	[OSMO_IPA_KA_S_INIT] = {
 		.name = "INIT",
 		.in_event_mask = S(OSMO_IPA_KA_E_START),
-		.out_state_mask = S(OSMO_IPA_KA_S_WAIT_RESP),
+		.out_state_mask = S(OSMO_IPA_KA_S_WAIT_RESP) | S(OSMO_IPA_KA_S_INIT),
 		.action = ipa_ka_init,
 	},
 	[OSMO_IPA_KA_S_IDLE] = {