nimble/transport: Remove ACL pool if not used

This removes extra memory used by ACL pool structures if pool is not
used, i.e. count=0. This happens e.g. on combined build since both hs
and ll sides use msys instead of transport pool. This can also be set by
user if neither central nor peripheral role is enabled and ACL pool is
not needed.

nimble/transport/src/transport.c

@@ -71,9 +71,11 @@ static struct os_mempool pool_evt;
 static uint8_t pool_evt_lo_buf[ OS_MEMPOOL_BYTES(POOL_EVT_LO_COUNT, POOL_EVT_SIZE) ];
 static struct os_mempool pool_evt_lo;
 
+#if POOL_ACL_COUNT > 0
 static uint8_t pool_acl_buf[ OS_MEMPOOL_BYTES(POOL_ACL_COUNT, POOL_ACL_SIZE) ];
 static struct os_mempool_ext pool_acl;
 static struct os_mbuf_pool mpool_acl;
+#endif
 
 static os_mempool_put_fn *transport_put_acl_from_ll_cb;
 
@@ -134,6 +136,7 @@ ble_transport_alloc_evt(int discardable)
 struct os_mbuf *
 ble_transport_alloc_acl_from_hs(void)
 {
+#if POOL_ACL_COUNT > 0
     struct os_mbuf *om;
     struct os_mbuf_pkthdr *pkthdr;
     uint16_t usrhdr_len;
@@ -151,11 +154,15 @@ ble_transport_alloc_acl_from_hs(void)
     }
 
     return om;
+#else
+    return NULL;
+#endif
 }
 
 struct os_mbuf *
 ble_transport_alloc_acl_from_ll(void)
 {
+#if POOL_ACL_COUNT > 0
     struct os_mbuf *om;
     struct os_mbuf_pkthdr *pkthdr;
 
@@ -166,6 +173,9 @@ ble_transport_alloc_acl_from_ll(void)
     }
 
     return om;
+#else
+    return NULL;
+#endif
 }
 
 void
@@ -202,6 +212,7 @@ ble_transport_ipc_free(void *buf)
     }
 }
 
+#if POOL_ACL_COUNT > 0
 static os_error_t
 ble_transport_acl_put(struct os_mempool_ext *mpe, void *data, void *arg)
 {
@@ -235,6 +246,7 @@ ble_transport_acl_put(struct os_mempool_ext *mpe, void *data, void *arg)
 
     return err;
 }
+#endif
 
 void
 ble_transport_init(void)
@@ -255,6 +267,7 @@ ble_transport_init(void)
                          pool_evt_lo_buf, "transport_pool_evt_lo");
     SYSINIT_PANIC_ASSERT(rc == 0);
 
+#if POOL_ACL_COUNT > 0
     rc = os_mempool_ext_init(&pool_acl, POOL_ACL_COUNT, POOL_ACL_SIZE,
                              pool_acl_buf, "transport_pool_acl");
     SYSINIT_PANIC_ASSERT(rc == 0);
@@ -264,6 +277,7 @@ ble_transport_init(void)
     SYSINIT_PANIC_ASSERT(rc == 0);
 
     pool_acl.mpe_put_cb = ble_transport_acl_put;
+#endif
 }
 
 int