libzfs: migrate single-use libzfs_set_pipe_max() to libzfs_core

Notably, this also means that the pipe is expanded before each
dataset is received, so updates to /p/s/f/pipe-max-size are reflected
for each new dataset

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13133

lib/libzfs/os/freebsd/libzfs_compat.c

@@ -38,12 +38,6 @@
 #define	ZFS_KMOD	"openzfs"
 #endif
 
-void
-libzfs_set_pipe_max(int infd)
-{
-	/* FreeBSD automatically resizes */
-	(void) infd;
-}
 
 static int
 execvPe(const char *name, const char *path, char * const *argv,