libipsec: Move restrictions regarding UDP encapsulation to users

src/frontends/android/app/src/main/jni/libandroidbridge/kernel/android_ipsec.c

@@ -71,6 +71,12 @@ METHOD(kernel_ipsec_t, add_sa, status_t,
 	private_kernel_android_ipsec_t *this, kernel_ipsec_sa_id_t *id,
 	kernel_ipsec_add_sa_t *data)
 {
+	if (!data->encap)
+	{
+		DBG1(DBG_ESP, "failed to add SAD entry: only UDP encapsulation is "
+			 "supported");
+		return FAILED;
+	}
 	return ipsec->sas->add_sa(ipsec->sas, id->src, id->dst, id->spi, id->proto,
 					data->reqid, id->mark, data->tfc, data->lifetime,
 					data->enc_alg, data->enc_key, data->int_alg, data->int_key,
@@ -82,6 +88,12 @@ METHOD(kernel_ipsec_t, update_sa, status_t,
 	private_kernel_android_ipsec_t *this, kernel_ipsec_sa_id_t *id,
 	kernel_ipsec_update_sa_t *data)
 {
+	if (!data->new_encap)
+	{
+		DBG1(DBG_ESP, "failed to update SAD entry: can't deactivate UDP "
+			 "encapsulation");
+		return NOT_SUPPORTED;
+	}
 	return ipsec->sas->update_sa(ipsec->sas, id->spi, id->proto, data->cpi,
 					id->src, id->dst, data->new_src, data->new_dst, data->encap,
 					data->new_encap, id->mark);

src/libcharon/plugins/kernel_libipsec/kernel_libipsec_ipsec.c

@@ -263,6 +263,12 @@ METHOD(kernel_ipsec_t, add_sa, status_t,
 	private_kernel_libipsec_ipsec_t *this, kernel_ipsec_sa_id_t *id,
 	kernel_ipsec_add_sa_t *data)
 {
+	if (!data->encap)
+	{
+		DBG1(DBG_ESP, "failed to add SAD entry: only UDP encapsulation is "
+			 "supported");
+		return FAILED;
+	}
 	return ipsec->sas->add_sa(ipsec->sas, id->src, id->dst, id->spi, id->proto,
 					data->reqid, id->mark, data->tfc, data->lifetime,
 					data->enc_alg, data->enc_key, data->int_alg, data->int_key,

src/libipsec/ipsec_sa_mgr.c

@@ -518,12 +518,6 @@ METHOD(ipsec_sa_mgr_t, add_sa, status_t,
 	DBG2(DBG_ESP, "  using integrity algorithm %N with key size %d",
 		 integrity_algorithm_names, int_alg, int_key.len * 8);
 
-	if (!encap)
-	{
-		DBG1(DBG_ESP, "  IPsec SA: only UDP encapsulation is supported");
-		return FAILED;
-	}
-
 	sa_new = ipsec_sa_create(spi, src, dst, protocol, reqid, mark, tfc,
 							 lifetime, enc_alg, enc_key, int_alg, int_key, mode,
 							 ipcomp, cpi, encap, esn, inbound);
@@ -574,13 +568,6 @@ METHOD(ipsec_sa_mgr_t, update_sa, status_t,
 	DBG2(DBG_ESP, "updating SAD entry with SPI %.8x from %#H..%#H to %#H..%#H",
 		 ntohl(spi), src, dst, new_src, new_dst);
 
-	if (!new_encap)
-	{
-		DBG1(DBG_ESP, "failed to update SAD entry: can't deactivate UDP "
-			 "encapsulation");
-		return NOT_SUPPORTED;
-	}
-
 	this->mutex->lock(this->mutex);
 	if (this->sas->find_first(this->sas, match_entry_by_spi_src_dst_cb,
 							 (void**)&entry, spi, src, dst) &&