ethernet: fix some bugs in ethernet driver

1. create a new pbuf to squash linked pbuf
2. optimize emac driver by adding ESP_IRAM_ATTR
3. remove duplicated function declare in esp_eth.h
4. remove duplicated code in emac_setup_tx_desc
5. disable Promiscuous mode

components/ethernet/emac_dev.c

@@ -111,5 +111,4 @@ void emac_mac_init(void)
     REG_SET_BIT(EMAC_GMACCONFIG_REG, EMAC_EMACDUPLEX);
     REG_SET_BIT(EMAC_GMACCONFIG_REG, EMAC_EMACMII);
     REG_CLR_BIT(EMAC_GMACCONFIG_REG, EMAC_EMACFESPEED);
-    REG_SET_BIT(EMAC_GMACFF_REG, EMAC_PMODE);
 }