[syslog] Handle backspace characters

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/lineconsole.c

 	if ( character < 0 )
 		return 0;
 
+	/* Handle backspace characters */
+	if ( character == '\b' ) {
+		if ( line->index )
+			line->index--;
+		return 0;
+	}
+
 	/* Ignore carriage return */
 	if ( character == '\r' )
 		return 0;