isisd: use IPv6 MTID for SRv6 locator TLVs when IPv6 MT is enabled

When IS-IS is configured with IPv6 Multi-Topology (topology ipv6-unicast),
SRv6 locator TLVs are still advertised with MTID 0 (ISIS_MT_STANDARD).
This patch makes SRv6 locator TLVs use the IPv6 MTID returned by
isis_area_ipv6_topology(area), so that they are consistent with IPv6
reachability TLVs and interoperable with implementations that expect
locators in the IPv6-unicast MT.

Signed-off-by: Kunio AKASHI <akashi004@gmail.com>

Author: k-akashi

isisd/isis_lsp.c

@@ -1236,7 +1236,7 @@ static void lsp_build(struct isis_lsp *lsp, struct isis_area *area)
 			listnode_add(locator.srv6_sid, sid);
 		}
 
-		isis_tlvs_add_srv6_locator(lsp->tlvs, 0, &locator);
+		isis_tlvs_add_srv6_locator(lsp->tlvs, isis_area_ipv6_topology(area), &locator);
 		lsp_debug("ISIS (%s): Adding SRv6 Locator information",
 			  area->area_tag);