selftests: forwarding: lib: Add helpers to build IGMP/MLD leave packets

The testsuite that checks for mcast_max_groups functionality will need to
wipe the added groups as well. Add helpers to build an IGMP or MLD packets
announcing that host is leaving a given group.
Signed-off-by: Petr Machata <petrm@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/forwarding/lib.sh

@@ -1794,6 +1794,21 @@ igmpv3_is_in_get()
 	payload_template_expand_checksum "$igmpv3" $checksum
 }
 
+igmpv2_leave_get()
+{
+	local GRP=$1; shift
+
+	local payload=$(:
+		)"17:"$(			: Type - Leave Group
+		)"00:"$(			: Max Resp Time - not meaningful
+		)"CHECKSUM:"$(			: Checksum
+		)"$(ipv4_to_bytes $GRP)"$(	: Group Address
+		)
+	local checksum=$(payload_template_calc_checksum "$payload")
+
+	payload_template_expand_checksum "$payload" $checksum
+}
+
 mldv2_is_in_get()
 {
 	local SIP=$1; shift
@@ -1837,3 +1852,38 @@ mldv2_is_in_get()
 
 	payload_template_expand_checksum "$hbh$icmpv6" $checksum
 }
+
+mldv1_done_get()
+{
+	local SIP=$1; shift
+	local GRP=$1; shift
+
+	local hbh
+	local icmpv6
+
+	hbh=$(:
+		)"3a:"$(			: Next Header - ICMPv6
+		)"00:"$(			: Hdr Ext Len
+		)"00:00:00:00:00:00:"$(		: Options and Padding
+		)
+
+	icmpv6=$(:
+		)"84:"$(			: Type - MLDv1 Done
+		)"00:"$(			: Code
+		)"CHECKSUM:"$(			: Checksum
+		)"00:00:"$(			: Max Resp Delay - not meaningful
+		)"00:00:"$(			: Reserved
+		)"$(ipv6_to_bytes $GRP):"$(	: Multicast address
+		)
+
+	local len=$(u16_to_bytes $(payload_template_nbytes $icmpv6))
+	local sudohdr=$(:
+		)"$(ipv6_to_bytes $SIP):"$(	: SIP
+		)"$(ipv6_to_bytes $GRP):"$(	: DIP is multicast address
+	        )"${len}:"$(			: Upper-layer length
+	        )"00:3a:"$(			: Zero and next-header
+	        )
+	local checksum=$(payload_template_calc_checksum ${sudohdr}${icmpv6})
+
+	payload_template_expand_checksum "$hbh$icmpv6" $checksum
+}