net: thunderbolt: Add comment clarifying prtcstns flags

ThunderboltIP protocol currently has two flags from which we only
support and set match frags ID. The first flag is reserved for full E2E
flow control. Add a comment that clarifies them.
Suggested-by: NYehezkel Bernat <yehezkelshb@gmail.com>
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: NYehezkel Bernat <YehezkelShB@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/thunderbolt.c

@@ -1335,6 +1335,10 @@ static int __init tbnet_init(void)
 	tb_property_add_immediate(tbnet_dir, "prtcid", 1);
 	tb_property_add_immediate(tbnet_dir, "prtcvers", 1);
 	tb_property_add_immediate(tbnet_dir, "prtcrevs", 1);
+	/* Currently only announce support for match frags ID (bit 1). Bit 0
+	 * is reserved for full E2E flow control which we do not support at
+	 * the moment.
+	 */
 	tb_property_add_immediate(tbnet_dir, "prtcstns",
 				  TBNET_MATCH_FRAGS_ID);