Add functions for filtered interfaces list

Add list_etcnet_iface_filtered() function.
This function prints iface name if filter_func returns
TRUE. Filter function will be called with an interface directory as first
parameter and all additional parameters with which list_etcnet_iface_filtered()
was called.

alterator-net-functions/alterator-net-functions

@@ -543,7 +543,37 @@ next_ppp()
     next_iface ppp 1
 }
 
+### filter functions
+__filter_etcnet_iface_default()
+{
+	local ifname="${1##*/}"
+	[ -n "$ifname" -a "$ifname" != "lo" -a "$ifname" != "default" -a "$ifname" != "unknown" ]
+}
+
 ### list various interface types
+# list_etcnet_iface_filtered [ ifaces_dir [ filter_func [ filter_func params ... ]]]
+#
+# list_etcnet_iface_filtered() prints iface name if filter_func returns TRUE
+# filter_func will be called with an interface directory as first parameter and
+# all additional parameters with which list_etcnet_iface_filtered() was called
+list_etcnet_iface_filtered()
+{
+	local dir="${1:-$etcnet_iface_dir}"
+	local filter_func="${2:-__filter_etcnet_iface_default}"
+	local i=
+
+	# Shift parameters for posterior filter_func call
+	if [ $# -gt 2 ]; then
+		shift 2
+	else
+		shift $#
+	fi
+
+	for i in $(find "$dir" -mindepth 1 -maxdepth 1 -type d 2>/dev/null); do
+		$filter_func "$i" $@ >/dev/null || continue
+		echo "${i##*/}"
+	done
+}
 
 list_ppp()
 {