Prototype support for /etc/netork/interfaces

This patch adds prototype support for the Debian/Ubuntu/Busybox network
configuration file /etc/netork/interfaces.  If this file exists Finit
will call `ifup` for each (non-commented-out) interface marked `auto`.

With this implementation we block boot until all ifup commands have
returned, which is less than ideal.  A better approach would be to ifup
only loopback and create deferred tasklets to be run in parallel with
the rest of the boot.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

helpers.c

@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 
+#include <ctype.h>		/* isblank() */
 #include <errno.h>
 #include <grp.h>
 #include <pwd.h>
@@ -39,6 +40,23 @@
 #include "helpers.h"
 #include "private.h"
 
+char *strip_line(char *line)
+{
+	char *ptr;
+
+	/* Trim leading whitespace */
+	while (*line && isblank(*line))
+		line++;
+
+	/* Strip any comment at end of line */
+	ptr = line;
+	while (*ptr && *ptr != '#')
+		ptr++;
+	*ptr = 0;
+
+	return line;
+}
+
 static int encode(int lvl)
 {
 	if (!lvl) return 0;