Changes from rc3:
* zvol IO can overflow the stack (M1)
* encrypted zvol clones did not get /dev/diskX
* zfs_replay could panic with NULL kcred
* update undo of decmpfs
MD5 (OpenZFSonOsX-2.1.0rc4-Catalina-10.15.pkg) = f8bba3df128c7182482a0a799f377071
MD5 (OpenZFSonOsX-2.1.0rc4-Big.Sur-11.pkg) = 34fd8d7117d3b0e673f7cc2de15d52fb
MD5 (OpenZFSonOsX-2.1.0rc4-Big.Sur-11-arm64.pkg) = a60f12f18baa696048774f84114c6f2d
MD5 (OpenZFSonOsX-2.1.0rc4-Mojave-10.14.pkg) = 0d27fb3cfe5bb18ff2f29597e2d77118