Rename aiocblist to kaiocb and use consistent variable names.

Typically <foo>list is used for a structure that holds a list head in
FreeBSD, not for members of a list.  As such, rename 'struct aiocblist'
to 'struct kaiocb' (the kernel version of 'struct aiocb').

While here, use more consistent variable names for AIO control blocks:

- Use 'job' instead of 'aiocbe', 'cb', 'cbe', or 'iocb' for kernel job
  objects.
- Use 'jobn' instead of 'cbn' for use with TAILQ_FOREACH_SAFE().
- Use 'sjob' and 'sjobn' instead of 'scb' and 'scbn' for fsync jobs.
- Use 'ujob' instead of 'aiocbp', 'job', 'uaiocb', or 'uuaiocb' to hold
  a user pointer to a 'struct aiocb'.
- Use 'ujobp' instead of 'aiocbp' for a user pointer to a 'struct aiocb *'.

Reviewed by:	kib
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D5125

sys/sys/event.h

@@ -222,7 +222,7 @@ struct knote {
 	union {
 		struct		file *p_fp;	/* file data pointer */
 		struct		proc *p_proc;	/* proc pointer */
-		struct		aiocblist *p_aio;	/* AIO job pointer */
+		struct		kaiocb *p_aio;	/* AIO job pointer */
 		struct		aioliojob *p_lio;	/* LIO job pointer */
 		sbintime_t	*p_nexttime;	/* next timer event fires at */
 		void		*p_v;		/* generic other pointer */

sys/sys/socketvar.h

@@ -104,7 +104,7 @@ struct socket {
 	struct	sigio *so_sigio;	/* [sg] information for async I/O or
 					   out of band data (SIGURG) */
 	u_long	so_oobmark;		/* (c) chars to oob mark */
-	TAILQ_HEAD(, aiocblist) so_aiojobq; /* AIO ops waiting on socket */
+	TAILQ_HEAD(, kaiocb) so_aiojobq; /* AIO ops waiting on socket */
 
 	struct sockbuf so_rcv, so_snd;