/*
* Macros for mbuf external storage.
*
* MCLGET allocates and adds an mbuf cluster to a normal mbuf;
* the flag M_EXT is set upon success.
*
* MEXTMALLOC allocates external storage and adds it to
* a normal mbuf; the flag M_EXT is set upon success.
*
* MEXTADD adds pre-allocated external storage to
* a normal mbuf; the flag M_EXT is set upon success.
*/