selftests: forwarding: lib: Add helpers for IP address handling

In order to generate IGMPv3 and MLDv2 packets on the fly, we will need
helpers to expand IPv4 and IPv6 addresses given as parameters in
mausezahn payload notation. Add helpers that do it.
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

@@ -1672,6 +1672,43 @@ hw_stats_monitor_test()
 	log_test "${type}_stats notifications"
 }
 
+ipv4_to_bytes()
+{
+	local IP=$1; shift
+
+	printf '%02x:' ${IP//./ } |
+	    sed 's/:$//'
+}
+
+# Convert a given IPv6 address, `IP' such that the :: token, if present, is
+# expanded, and each 16-bit group is padded with zeroes to be 4 hexadecimal
+# digits. An optional `BYTESEP' parameter can be given to further separate
+# individual bytes of each 16-bit group.
+expand_ipv6()
+{
+	local IP=$1; shift
+	local bytesep=$1; shift
+
+	local cvt_ip=${IP/::/_}
+	local colons=${cvt_ip//[^:]/}
+	local allcol=:::::::
+	# IP where :: -> the appropriate number of colons:
+	local allcol_ip=${cvt_ip/_/${allcol:${#colons}}}
+
+	echo $allcol_ip | tr : '\n' |
+	    sed s/^/0000/ |
+	    sed 's/.*\(..\)\(..\)/\1'"$bytesep"'\2/' |
+	    tr '\n' : |
+	    sed 's/:$//'
+}
+
+ipv6_to_bytes()
+{
+	local IP=$1; shift
+
+	expand_ipv6 "$IP" :
+}
+
 igmpv3_is_in_get()
 {
 	local igmpv3