xfs: restore nofs context unconditionally in xfs_trans_roll

In the Linux kernel, the following vulnerability has been resolved:

xfs: restore nofs context unconditionally in xfs_trans_roll

When __xfs_trans_commit() fails in xfs_trans_roll(), the NOFS context
is cleared but only restored in the success path. This leaves the
error path without nofs protection, causing a circular lock dependency
between xfs_nondir_ilock_class and fs_reclaim:

CPU0 CPU1
---- ----
lock(&xfs_nondir_ilock_class);
lock(fs_reclaim);
lock(&xfs_nondir_ilock_class);
lock(fs_reclaim);

Fix this by moving xfs_trans_set_context() before the error check so
that nofs context is always restored on the new transaction.