announce reattach fix (ARMmbed#1873)

Thread device attempts to reattach using parent request
after hearing an announce

source/6LoWPAN/Thread/thread_bootstrap.c

@@ -2149,6 +2149,12 @@ static bool thread_bootstrap_sync_after_reset_start(protocol_interface_info_entr
     uint16_t my_short_address;
     uint8_t parent_mac64[8];
 
+    // link sync is allowed only once in bootstrap start and we might get here in other cases also
+    if (!cur->thread_info->link_sync_allowed) {
+        return false;
+    }
+    cur->thread_info->link_sync_allowed = false;
+
     int link_info_err = thread_nvm_store_link_info_get(parent_mac64, &my_short_address);
     if ( link_info_err!= THREAD_NVM_FILE_SUCCESS) {
         tr_warning("thread_nvm_store_link_info_get returned %d", link_info_err);
@@ -2157,7 +2163,7 @@ static bool thread_bootstrap_sync_after_reset_start(protocol_interface_info_entr
     link_info_err = thread_nvm_store_link_info_clear();
     if ( link_info_err!= THREAD_NVM_FILE_SUCCESS) {
         tr_warning("thread_nvm_store_link_info_clear returned %d", link_info_err);
-        }
+    }
     if (thread_is_router_addr(my_short_address)) {
         thread_info(cur)->routerShortAddress = my_short_address;
         thread_dynamic_storage_build_mle_table(cur->id);

source/6LoWPAN/Thread/thread_common.c

@@ -226,6 +226,7 @@ int8_t thread_bootstrap_up(protocol_interface_info_entry_t *cur)
     ret_val = nwk_6lowpan_up(cur);
 
     cur->nwk_nd_re_scan_count = 0;
+    cur->thread_info->link_sync_allowed = true;
 
     return ret_val;
 }

source/6LoWPAN/Thread/thread_common.h

@@ -328,6 +328,7 @@ typedef struct thread_info_s {
     bool networkDataRequested: 1;
     bool end_device_link_synch: 1;
     bool router_mc_addrs_registered: 1;
+    bool link_sync_allowed:1;
     bool leader_synced:1; // flag used by leader after restart
 } thread_info_t;