various: split functions to IPv4 and IPv6 versions

The code selection will be set with function pointer, which avoids
numerous IP version checks.  As a result with some inputs the analysis
runs quicker.  Most users will not notice much of difference.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

src/dhcpd-pools.c

@@ -248,7 +248,7 @@ int main(int argc, char **argv)
 
 	/* Do the job */
 	prepare_memory();
-	xstrstr = xstrstr_init;
+	set_ipv_functions(VERSION_UNKNOWN);
 	parse_config(true, config.dhcpdconf_file, shared_networks);
 
 	parse_leases();