Merge pull request #11420 from tymoteuszblochmobica/cm3ds

Fixed smsc9220_emac link_out memory management.

Author: 0xc0170

features/netsocket/emac-drivers/TARGET_ARM_SSG/COMPONENT_SMSC9220/smsc9220_emac.cpp

@@ -168,6 +168,7 @@ bool SMSC9220_EMAC::link_out(emac_mem_buf_t *buf)
                                       true,
                                       (const char*)_memory_manager->get_ptr(buf),
                                       _memory_manager->get_len(buf));
+        _memory_manager->free(buf);
         if (error != SMSC9220_ERROR_NONE) {
             _TXLockMutex.unlock();
             return false;