gfs2: Fix debugfs glocks dump

gfs2: Fix debugfs glocks dump

The switch to rhashtables (commit 88ffbf3e03) broke the debugfs glock
dump (/sys/kernel/debug/gfs2/<device>/glocks) for dumps bigger than a
single buffer: the right function for restarting an rhashtable iteration
from the beginning of the hash table is rhashtable_walk_enter;
rhashtable_walk_stop + rhashtable_walk_start will just resume from the
current position.

Signed-off-by: Andreas Gruenbacher <[email protected]>
Signed-off-by: Bob Peterson <[email protected]>
Cc: [email protected] # v4.3+