linux: module: weld all but spl.ko into zfs.ko

Originally it was thought it would be useful to split up the kmods
by functionality.  This would allow external consumers to only load
what was needed.  However, in practice we've never had a case where
this functionality would be needed, and conversely managing multiple
kmods can be awkward.  Therefore, this change merges all but the
spl.ko kmod in to a single zfs.ko kmod.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13274

tests/zfs-tests/include/libtest.shlib

@@ -3264,7 +3264,6 @@ function set_tunable_impl
 	typeset name="$1"
 	typeset value="$2"
 	typeset mdb_cmd="$3"
-	typeset module="${4:-zfs}"
 
 	eval "typeset tunable=\$$name"
 	case "$tunable" in
@@ -3283,14 +3282,13 @@ function set_tunable_impl
 
 	case "$UNAME" in
 	Linux)
-		typeset zfs_tunables="/sys/module/$module/parameters"
+		typeset zfs_tunables="/sys/module/zfs/parameters"
 		echo "$value" >"$zfs_tunables/$tunable"
 		;;
 	FreeBSD)
 		sysctl vfs.zfs.$tunable=$value
 		;;
 	SunOS)
-		[[ "$module" -eq "zfs" ]] || return 1
 		echo "${tunable}/${mdb_cmd}0t${value}" | mdb -kw
 		;;
 	esac