tcpip_callbackmsg_new() function

Allocate a structure for a static callback message and initialize it. The message has a special type such that lwIP never frees it. This is intended to be used to send "static" messages from interrupt context, e.g. the message is allocated once and posted several times from an IRQ using tcpip_callbackmsg_trycallback(). Example usage: Trigger execution of an ethernet IRQ DPC routine in lwIP thread context. @see tcpip_callbackmsg_trycallback() @see tcpip_callbackmsg_delete()