Add support for Realtek (Ethertype) DSA data

Realtek switchtag rtl4a (4 bytes long, protocol 0xA) and rtl8_4 (8 bytes
long, protocol 0x04) are Ethertype DSA tags, inserted in the Ethernet
header similar to an 802.1Q tag. Both shares the same Ethertype 0x8899
as other Realtek proprietary protocols.

Realtek switchtag rtl8_4t is identical to rtl8_4 but positioned before
the CRC, at the end of the Ethernet frame.

Author: luizluca

pcap-linux.c

@@ -5048,6 +5048,9 @@ static struct dsa_proto {
 	{ "brcm-prepend", DLT_DSA_TAG_BRCM_PREPEND },
 	{ "dsa", DLT_DSA_TAG_DSA },
 	{ "edsa", DLT_DSA_TAG_EDSA },
+	{ "rtl4a", DLT_EN10MB },
+	{ "rtl8_4", DLT_EN10MB },
+	{ "rtl8_4t", DLT_EN10MB },
 };
 
 static int